Light detection system, discharge probability calculating method, and received light quantity measuring method

ABSTRACT

To calculate received light quantity even when part of noise component&#39;s discharge probability is unknown, a light detection system includes a discharge probability calculating portion that calculates discharge probabilities for a first state in which a source&#39;s light with known light quantity impinges on an optical sensor, a second state in which the source&#39;s turning-on/turning-off state is the same as the first state with a drive pulse width applied to the optical sensor different from the first state, a third state in which the source&#39;s turning-on/turning-off state is different from the first and second states with the same pulse width as the first state, and a fourth state in which the source&#39;s turning-on/turning-off state is the same as the third state with the same pulse width as the second state, another discharge probability calculating portion that calculates regular and irregular discharges&#39; probabilities, and a received light quantity calculating portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of foreign priority to Japanese Patent Application No. JP 2020-025479 filed on Feb. 18, 2020, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present disclosure relates to a light detection system configured to detect light such as a flame.

As an optical sensor configured to detect the presence or absence of a flame based on ultraviolet rays emitted from light of the flame in a combustion furnace or the like, a photoelectric tube type ultraviolet sensor may be used. It has been observed that an irregular discharge phenomenon (pseudo discharge) caused by a noise component other than a discharge occurring due to a photoelectric effect occurs in discharge of the photoelectric tube type ultraviolet sensor.

PTL 1 proposes a flame detection system in which a pulse width of a drive pulse to be applied to an optical sensor is controlled to obtain a received light quantity of the discharge from a calculation so that a life of a flame sensor can be determined based on a light quantity. However, the discharge of the actual optical sensor includes an irregular discharge caused by a noise, which is generally referred to as a failure, and thus there is a case where the discharge occurs even when light generated by the flame does not exist and causes erroneous detection. In order to eliminate such an erroneous detection of a discharge, it is necessary to consider a method of measuring a discharge probability in consideration of a noise component.

Further, in a flame detection system disclosed in PTL 2, a method of obtaining the received light quantity in consideration of a discharge probability of a noise component other than a regular discharge is proposed, which enables accurate detection of the presence or absence of a flame. However, in the flame detection system disclosed in PTL 2, the discharge probability of the noise component needs to be known.

Further, in a failure detecting device disclosed in PTL 3, it has been proposed to provide a shutter mechanism configured to block an electromagnetic wave incident on an optical sensor to detect a failure due to a self discharge of the optical sensor. However, in the failure detecting device disclosed in PTL 3, there is no discriminating method for distinguishing between the regular discharge and the irregular discharge with the change in measurement sensitivity due to the life of the optical sensor, and thus there is a possibility of erroneous detection of the failure.

It should be noted that the above problems occur not only in the flame detection system but also in the light detection system using the optical sensor.

CITATION LIST Patent Literature

[PTL 1] JP-A-2018-84422

[PTL 2] JP-A-2018-84423

[PTL 3] JP-A-05-012581

BRIEF SUMMARY OF THE INVENTION

The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to provide a light detection system and a discharge probability calculating method capable of calculating a discharge probability of a regular discharge excluding a noise component other than a discharge occurring due to a photoelectric effect of an optical sensor, and a discharge probability of an irregular discharge caused by the noise component, which occurs depending on a received light quantity received by the optical sensor.

Another object of the present disclosure is to provide a light detection system and a received light quantity measuring method capable of calculating a received light quantity even when a part of a discharge probability of a noise component is an unknown number.

A light detection system (a first embodiment) of the present disclosure includes: an optical sensor configured to detect light emitted from a first light source; a second light source having a known light quantity, which is installed such that generated light is incident on the optical sensor together with the light from the first light source; a light source control portion configured to control turning-on/turning-off of the second light source; an application voltage generating portion configured to periodically apply a drive pulse voltage to an electrode of the optical sensor; a current detecting portion configured to detect a discharge current of the optical sensor; a discharge determining portion configured to detect a discharge of the optical sensor based on the discharge current detected by the current detecting portion; a first discharge probability calculating portion configured to calculate a discharge probability based on the number of times of application of the drive pulse voltage applied by the application voltage generating portion and the number of times of discharge detected by the discharge determining portion during the application of the drive pulse voltage for each of a first state in which the second light source is turned on or turned off, a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state, a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as that of the first state, and a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is the same as that of the second state; a storing portion configured to store, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first and second states, and the third and fourth states; a second discharge probability calculating portion configured to calculate a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the first, second, third, and fourth states, and the pulse widths of the drive pulse voltage in the first, second, third, and fourth states; and a received light quantity calculating portion configured to calculate the received light quantity received by the optical sensor in the first and second states or the third and fourth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the first, second, third, and fourth states, the pulse widths of the drive pulse voltage in the first, second, third, and fourth states, and the discharge probabilities calculated by the second discharge probability calculating portion.

Further, a light detection system (the first embodiment) of the present disclosure includes: an optical sensor configured to detect light emitted from a first light source; a second light source having a known light quantity, which is installed such that generated light is incident on the optical sensor together with the light from the first light source; a light source control portion configured to control turning-on/turning-off of the second light source; an application voltage generating portion configured to periodically apply a drive pulse voltage to an electrode of the optical sensor; a current detecting portion configured to detect a discharge current of the optical sensor; a discharge determining portion configured to detect a discharge of the optical sensor based on the discharge current detected by the current detecting portion; a first discharge probability calculating portion configured to calculate a discharge probability based on the number of times of application of the drive pulse voltage applied by the application voltage generating portion and the number of times of discharge detected by the discharge determining portion during the application of the drive pulse voltage for each of a first state in which the second light source is turned on or turned off, a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state, a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as that of the first state, a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is the same as that of the second state, a fifth state in which a turning-on/turning-off state of the second light source is the same as that of the first and second states, and a pulse width of the drive pulse voltage is the same as that of either the first and third states or the second and fourth states, or different from that of all of the first, second, third, and fourth states, and a sixth state in which a turning-on/turning-off state of the second light source is the same as that of the third and fourth states and a pulse width of the drive pulse voltage is the same as that of the fifth state; a storing portion configured to store, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first, second, and fifth states, and the third, fourth, and sixth states; a second discharge probability calculating portion configured to calculate a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the first, second, third, fourth, fifth, and sixth states, and the pulse widths of the drive pulse voltage in the first, second, third, fourth, fifth, and sixth states; and a received light quantity calculating portion configured to calculate the received light quantity received by the optical sensor in the fifth and sixth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the fifth and sixth states, the pulse widths of the drive pulse voltage in the fifth and sixth states, and the discharge probabilities calculated by the second discharge probability calculating portion.

Further, a light detection system (a second embodiment) of the present disclosure includes: an optical sensor configured to detect light emitted from a first light source; a second light source having a known light quantity, which is installed such that generated light is incident on the optical sensor together with the light from the first light source; a light source control portion configured to control turning-on/turning-off of the second light source; an application voltage generating portion configured to periodically apply a drive pulse voltage to an electrode of the optical sensor; a current detecting portion configured to detect a discharge current of the optical sensor; a discharge determining portion configured to detect a discharge of the optical sensor based on the discharge current detected by the current detecting portion; a first discharge probability calculating portion configured to calculate a discharge probability based on the number of times of application of the drive pulse voltage applied by the application voltage generating portion and the number of times of discharge detected by the discharge determining portion during the application of the drive pulse voltage for each of a first state in which the second light source is turned on or turned off, a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state, a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as or different from that of the first state, a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is different from that of the third state, a fifth state in which a turning-on/turning-off state of the second light source is the same as that of the first and second states, and a pulse width of the drive pulse voltage is the same as that of at least one of the first, second, third, and fourth states or different from that of all of the first, second, third, and fourth states, and a sixth state in which a turning-on/turning-off state of the second light source is the same as that of the third and fourth states and a pulse width of the drive pulse voltage is the same as that of the fifth state; a storing portion configured to store, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first, second, and fifth states, and the third, fourth, and sixth states; and a second discharge probability calculating portion configured to calculate a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the first, second, third, fourth, fifth, and sixth states, and the pulse widths of the drive pulse voltage in the first, second, fifth, and sixth states under a condition that a difference in pulse width between the first state and the second state is equal to a difference in pulse width between the third state and the fourth state.

Further, one configuration example of the light detection system (the second embodiment) of the present disclosure further includes: a received light quantity calculating portion configured to calculate the received light quantity received by the optical sensor in the fifth and sixth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the fifth and sixth states, the pulse widths of the drive pulse voltage in the fifth and sixth states, and the discharge probabilities calculated by the second discharge probability calculating portion.

Further, a received light quantity measuring method of a light detection system (the first embodiment) of the present disclosure includes: a first step of periodically applying a drive pulse voltage to an electrode of an optical sensor that detects light emitted from a first light source in a first state in which light from a second light source having a known light quantity is incident on the optical sensor or the second light source is turned off; a second step of detecting a discharge current of the optical sensor in the first state; a third step of detecting a discharge of the optical sensor based on the discharge current in the first state; a fourth step of calculating a discharge probability in the first state based on the number of times of application of the drive pulse voltage applied in the first step and the number of times of discharge detected in the third step during the application of the drive pulse voltage; a fifth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state; a sixth step of detecting a discharge current of the optical sensor in the second state; a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state; an eighth step of calculating a discharge probability in the second state based on the number of times of application of the drive pulse voltage applied in the fifth step and the number of times of discharge detected in the seventh step during the application of the drive pulse voltage; a ninth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as that of the first state; a tenth step of detecting a discharge current of the optical sensor in the third state; an eleventh step of detecting a discharge of the optical sensor based on the discharge current in the third state; a twelfth step of calculating a discharge probability in the third state based on the number of times of application of the drive pulse voltage applied in the ninth step and the number of times of discharge detected in the eleventh step during the application of the drive pulse voltage; a thirteenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is the same as that of the second state; a fourteenth step of detecting a discharge current of the optical sensor in the fourth state; a fifteenth step of detecting a discharge of the optical sensor based on the discharge current in the fourth state; a sixteenth step of calculating a discharge probability in the fourth state based on the number of times of application of the drive pulse voltage applied in the thirteenth step and the number of times of discharge detected in the fifteenth step during the application of the drive pulse voltage; a seventeenth step of referring to a storing portion that stores, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first and second states and the third and fourth states, and calculating a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth, eighth, twelfth, and sixteenth steps, and the pulse widths of the drive pulse voltage in the first, second, third, and fourth states; and an eighteenth step of calculating the received light quantity received by the optical sensor in the first and second states or the third and fourth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth, eighth, twelfth, and sixteenth steps, the pulse widths of the drive pulse voltage in the first, second, third, and fourth states, and the discharge probabilities calculated in the seventeenth step.

Further, a received light quantity measuring method of a light detection system (the first embodiment) of the present disclosure includes: a first step of periodically applying a drive pulse voltage to an electrode of an optical sensor that detects light emitted from a first light source in a first state in which light from a second light source having a known light quantity is incident on the optical sensor or the second light source is turned off; a second step of detecting a discharge current of the optical sensor in the first state; a third step of detecting a discharge of the optical sensor based on the discharge current in the first state; a fourth step of calculating a discharge probability in the first state based on the number of times of application of the drive pulse voltage applied in the first step and the number of times of discharge detected in the third step during the application of the drive pulse voltage; a fifth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state; a sixth step of detecting a discharge current of the optical sensor in the second state; a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state; an eighth step of calculating a discharge probability in the second state based on the number of times of application of the drive pulse voltage applied in the fifth step and the number of times of discharge detected in the seventh step during the application of the drive pulse voltage; a ninth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as that of the first state; a tenth step of detecting a discharge current of the optical sensor in the third state; an eleventh step of detecting a discharge of the optical sensor based on the discharge current in the third state; a twelfth step of calculating a discharge probability in the third state based on the number of times of application of the drive pulse voltage applied in the ninth step and the number of times of discharge detected in the eleventh step during the application of the drive pulse voltage; a thirteenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is the same as that of the second state; a fourteenth step of detecting a discharge current of the optical sensor in the fourth state; a fifteenth step of detecting a discharge of the optical sensor based on the discharge current in the fourth state; a sixteenth step of calculating a discharge probability in the fourth state based on the number of times of application of the drive pulse voltage applied in the thirteenth step and the number of times of discharge detected in the fifteenth step during the application of the drive pulse voltage; a seventeenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fifth state in which a turning-on/turning-off state of the second light source is the same as that of the first and second states and a pulse width of the drive pulse voltage is the same as that of either the first and third states or the second and fourth states, or different from that of all of the first, second, third, and fourth states; an eighteenth step of detecting a discharge current of the optical sensor in the fifth state; a nineteenth step of detecting a discharge of the optical sensor based on the discharge current in the fifth state; a twentieth step of calculating a discharge probability in the fifth state based on the number of times of application of the drive pulse voltage applied in the seventeenth step and the number of times of discharge detected in the nineteenth step during the application of the drive pulse voltage; a twenty-first step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a sixth state in which a turning-on/turning-off state of the second light source is the same as that of the third and fourth states and a pulse width of the drive pulse voltage is the same as that of the fifth state; a twenty-second step of detecting a discharge current of the optical sensor in the sixth state; a twenty-third step of detecting a discharge of the optical sensor based on the discharge current in the sixth state; a twenty-fourth step of calculating a discharge probability in the sixth state based on the number of times of application of the drive pulse voltage applied in the twenty-first step and the number of times of discharge detected in the twenty-third step during the application of the drive pulse voltage; a twenty-fifth step of referring to a storing portion that stores, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first, second, and fifth states and the third, fourth, and sixth states, and calculating a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth, eighth, twelfth, sixteenth, twentieth, and twenty-fourth steps, and the pulse widths of the drive pulse voltage in the first, second, third, fourth, fifth, and sixth states; and a twenty-sixth step of calculating the received light quantity received by the optical sensor in the fifth and sixth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the twentieth and twenty-fourth steps, the pulse widths of the drive pulse voltage in the fifth and sixth states, and discharge probabilities calculated in the twenty-fifth step.

Further, a discharge probability calculating method of a light detection system (the second embodiment) of the present disclosure includes: a first step of periodically applying a drive pulse voltage to an electrode of an optical sensor that detects light emitted from a first light source in a first state in which light from a second light source having a known light quantity is incident on the optical sensor or the second light source is turned off; a second step of detecting a discharge current of the optical sensor in the first state; a third step of detecting a discharge of the optical sensor based on the discharge current in the first state; a fourth step of calculating a discharge probability in the first state based on the number of times of application of the drive pulse voltage applied in the first step and the number of times of discharge detected in the third step during the application of the drive pulse voltage; a fifth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state; a sixth step of detecting a discharge current of the optical sensor in the second state; a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state; an eighth step of calculating a discharge probability in the second state based on the number of times of application of the drive pulse voltage applied in the fifth step and the number of times of discharge detected in the seventh step during the application of the drive pulse voltage; a ninth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as or different from that of the first state; a tenth step of detecting a discharge current of the optical sensor in the third state; an eleventh step of detecting a discharge of the optical sensor based on the discharge current in the third state; a twelfth step of calculating a discharge probability in the third state based on the number of times of application of the drive pulse voltage applied in the ninth step and the number of times of discharge detected in the eleventh step during the application of the drive pulse voltage; a thirteenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is different from that of the third state; a fourteenth step of detecting a discharge current of the optical sensor in the fourth state; a fifteenth step of detecting a discharge of the optical sensor based on the discharge current in the fourth state; a sixteenth step of calculating a discharge probability in the fourth state based on the number of times of application of the drive pulse voltage applied in the thirteenth step and the number of times of discharge detected in the fifteenth step during the application of the drive pulse voltage; a seventeenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fifth state in which a turning-on/turning-off state of the second light source is the same as that of the first and second states and a pulse width of the drive pulse voltage is the same as that of at least one of the first, second, third, and fourth states or different from that of all of the first, second, third, and fourth states; an eighteenth step of detecting a discharge current of the optical sensor in the fifth state; a nineteenth step of detecting a discharge of the optical sensor based on the discharge current in the fifth state; a twentieth step of calculating a discharge probability in the fifth state based on the number of times of application of the drive pulse voltage applied in the seventeenth step and the number of times of discharge detected in the nineteenth step during the application of the drive pulse voltage; a twenty-first step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a sixth state in which a turning-on/turning-off state of the second light source is the same as that of the third and fourth states and a pulse width of the drive pulse voltage is the same as that of the fifth state; a twenty-second step of detecting a discharge current of the optical sensor in the sixth state; a twenty-third step of detecting a discharge of the optical sensor based on the discharge current in the sixth state; a twenty-fourth step of calculating a discharge probability in the sixth state based on the number of times of application of the drive pulse voltage applied in the twenty-first step and the number of times of discharge detected in the twenty-third step during the application of the drive pulse voltage; and a twenty-fifth step of referring to a storing portion that stores, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first, second, and fifth states and the third, fourth, and sixth states, and calculating a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth, eighth, twelfth, sixteenth, twentieth, and twenty-fourth steps, and the pulse widths of the drive pulse voltage in the first, second, fifth, and sixth states under a condition that a difference in pulse width between the first state and the second state is equal to a difference in pulse width between the third state and the fourth state.

Further, a received light quantity measuring method of a light detection system (the second embodiment) of the present disclosure includes: a first step of periodically applying a drive pulse voltage to an electrode of an optical sensor that detects light emitted from a first light source in a first state in which light from a second light source having a known light quantity is incident on the optical sensor or the second light source is turned off; a second step of detecting a discharge current of the optical sensor in the first state; a third step of detecting a discharge of the optical sensor based on the discharge current in the first state; a fourth step of calculating a discharge probability in the first state based on the number of times of application of the drive pulse voltage applied in the first step and the number of times of discharge detected in the third step during the application of the drive pulse voltage; a fifth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state; a sixth step of detecting a discharge current of the optical sensor in the second state; a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state; an eighth step of calculating a discharge probability in the second state based on the number of times of application of the drive pulse voltage applied in the fifth step and the number of times of discharge detected in the seventh step during the application of the drive pulse voltage; a ninth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as or different from that of the first state; a tenth step of detecting a discharge current of the optical sensor in the third state; an eleventh step of detecting a discharge of the optical sensor based on the discharge current in the third state; a twelfth step of calculating a discharge probability in the third state based on the number of times of application of the drive pulse voltage applied in the ninth step and the number of times of discharge detected in the eleventh step during the application of the drive pulse voltage; a thirteenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is different from that of the third state; a fourteenth step of detecting a discharge current of the optical sensor in the fourth state; a fifteenth step of detecting a discharge of the optical sensor based on the discharge current in the fourth state; a sixteenth step of calculating a discharge probability in the fourth state based on the number of times of application of the drive pulse voltage applied in the thirteenth step and the number of times of discharge detected in the fifteenth step during the application of the drive pulse voltage; a seventeenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fifth state in which a turning-on/turning-off state of the second light source is the same as that of the first and second states and a pulse width of the drive pulse voltage is the same as that of at least one of the first, second, third, and fourth states or different from that of all of the first, second, third, and fourth states; an eighteenth step of detecting a discharge current of the optical sensor in the fifth state; a nineteenth step of detecting a discharge of the optical sensor based on the discharge current in the fifth state; a twentieth step of calculating a discharge probability in the fifth state based on the number of times of application of the drive pulse voltage applied in the seventeenth step and the number of times of discharge detected in the nineteenth step during the application of the drive pulse voltage; a twenty-first step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a sixth state in which a turning-on/turning-off state of the second light source is the same as that of the third and fourth states and a pulse width of the drive pulse voltage is the same as that of the fifth state; a twenty-second step of detecting a discharge current of the optical sensor in the sixth state; a twenty-third step of detecting a discharge of the optical sensor based on the discharge current in the sixth state; a twenty-fourth step of calculating a discharge probability in the sixth state based on the number of times of application of the drive pulse voltage applied in the twenty-first step and the number of times of discharge detected in the twenty-third step during the application of the drive pulse voltage; a twenty-fifth step of referring to a storing portion that stores, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first, second, and fifth states and the third, fourth, and sixth states, and calculating a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth, eighth, twelfth, sixteenth, twentieth, and twenty-fourth steps, and the pulse widths of the drive pulse voltage in the first, second, fifth, and sixth states under a condition that a difference in pulse width between the first state and the second state is equal to a difference in pulse width between the third state and the fourth state; and a twenty-sixth step of calculating the received light quantity received by the optical sensor in the fifth and sixth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the twentieth and twenty-fourth steps, the pulse widths of the drive pulse voltage in the fifth and sixth states, and the discharge probabilities calculated in the twenty-fifth step.

According to the present disclosure, in addition to a first light source to be detected, by providing a second light source having a known light quantity and a light source control portion and by further providing an application voltage generating portion, a current detecting portion, a discharge determining portion, a first discharge probability calculating portion, a storing portion, a second discharge probability calculating portion, and a received light quantity calculating portion, even when at least one of a discharge probability of an irregular discharge caused by a noise component, which occurs depending on a pulse width of a drive pulse voltage and which occurs without depending on a received light quantity received by an optical sensor, and a discharge probability of an irregular discharge caused by the noise component, which occurs without depending on the pulse width of the drive pulse voltage and the received light quantity received by the optical sensor, is an unknown number, it is possible to calculate a received light quantity. As a result, in the present disclosure, it is possible to accurately detect the presence or absence of a flame by using the obtained received light quantity. Further, in the present disclosure, it is possible to reduce the possibility that the life of the optical sensor is erroneously determined by using the received light quantity.

Further, in the present disclosure, in addition to a first light source to be detected, by providing a second light source having a known light quantity and a light source control portion and by further providing an application voltage generating portion, a current detecting portion, a discharge determining portion, a first discharge probability calculating portion, a storing portion, and a second discharge probability calculating portion, it is possible to calculate a discharge probability of a regular discharge excluding a noise component other than a discharge occurring due to a photoelectric effect of an optical sensor and a discharge probability of an irregular discharge caused by the noise component, which occurs without depending on a pulse width of a drive pulse voltage and which occurs depending on a received light quantity received by the optical sensor. As a result, in the present disclosure, it is possible to implement a life determination of the optical sensor based on the discharge probability of the regular discharge and the discharge probability of the irregular discharge.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram illustrating a configuration of a light detection system according to a first embodiment of the present disclosure.

FIG. 2 is a waveform diagram illustrating a drive pulse applied to an optical sensor and a detected voltage detected in a current detecting circuit in the first embodiment of the present disclosure.

FIG. 3 is a flowchart explaining an operation of the light detection system according to the first embodiment of the present disclosure.

FIG. 4 is a flowchart explaining an operation of the light detection system according to the first embodiment of the present disclosure.

FIG. 5 is a flowchart explaining another operation of the light detection system according to the first embodiment of the present disclosure.

FIG. 6 is a flowchart explaining another operation of the light detection system according to the first embodiment of the present disclosure.

FIG. 7 is a block diagram illustrating a configuration of a light detection system according to a second embodiment of the present disclosure.

FIG. 8 is a flowchart explaining an operation of the light detection system according to the second embodiment of the present disclosure.

FIG. 9 is a block diagram illustrating a configuration example of a computer that implements the light detection system according to the first and second embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

Hereinafter, a method of measuring a regular discharge excluding a noise component and an irregular discharge caused by the noise component, and a method of measuring a received light quantity will be described. An optical sensor using a photoelectric effect is a photoelectric tube, which is energized by a photon hitting an electrode. The energization proceeds under the following conditions.

[Operation of Optical Sensor]

When a photon hits one of the electrodes in a state in which a voltage is applied between a pair of electrodes of an optical sensor, photoelectrons are emitted at a certain probability, and an electron avalanche of electrons is produced to cause energization (a discharge current flows between the electrodes).

While a voltage is applied between the electrodes, the optical sensor continues to be energized. Alternatively, when the energization of the optical sensor is confirmed, the voltage is lowered immediately, so that the energization is stopped. As described above, when the voltage between the electrodes decreases, the optical sensor terminates the energization.

When one photon hits the electrode of the optical sensor, the probability that the optical sensor discharges is defined as P₁.

Further, when two photons hit the electrode of the optical sensor, the probability that the optical sensor discharges is defined as P₂. Since P₂ is opposite to the probability that neither the first photon nor the second photon discharges, a relationship between P₂ and P₁ is expressed by Expression (1).

(1−P ₂)=(1−P ₁)²  (1)

In general, where P_(n) is the probability that the optical sensor discharges when n photons hit the electrode of the optical sensor, and P_(m) is the probability that the optical sensor discharges when m photons hit the electrode of the optical sensor (n and m are natural numbers), Expressions (2) and (3) are satisfied in the same manner as Expression (1).

(1−P _(n))=(1−P ₁)^(n)  (2)

(1−P _(m))=(1−P ₁)^(m)  (3)

From Expressions (2) and (3), Expression (4) is derived as a relationship between P_(n) and P_(m).

$\begin{matrix} {{\left( {1 - P_{n}} \right)^{\frac{1}{n}} = \left( {1 - P_{m}} \right)^{\frac{1}{m}}}{\left( {1 - P_{n}} \right)^{\frac{m}{n}} = \left( {1 - P_{m}} \right)}{\frac{m}{n} = {\log_{({1 - P_{n}})}\left( {1 - P_{m}} \right)}}} & (4) \end{matrix}$

Where E is the number of photons coming to the electrode of the optical sensor per unit time, and T is the time duration during which a voltage equal to or higher than a discharge starting voltage from the optical sensor is applied between the electrodes (hereinafter referred to as a “pulse width”), the number of photons that hit the electrode per every application of the voltage is expressed by ET. Accordingly, a relationship among the number of photons E, the pulse width T, and a discharge probability P when the same optical sensor is operated under a condition B which is different from a certain condition A is expressed by the following Expression (5). Here, when the number of photons to be used as a reference is defined as E₀ to establish Q=E/E₀, Expression (6) is obtained. Here, Q is referred to as a “received light quantity”.

$\begin{matrix} {\frac{E_{B}T_{B}}{E_{A}T_{A}} = {\log_{({1 - P_{A}})}\left( {1 - P_{B}} \right)}} & (5) \\ {\frac{Q_{B}T_{B}}{Q_{A}T_{A}} = {\log_{({1 - P_{A}})}\left( {1 - P_{B}} \right)}} & (6) \end{matrix}$

[Configuration and Operation of Light Detection System]

FIG. 1 is a block diagram illustrating a configuration of the light detection system according to the first embodiment of the present disclosure. The light detection system is configured to drive the optical sensor and calculate the discharge probability and the received light quantity from the light source based on a result of the driving of the optical sensor. The light detection system includes an optical sensor 1 configured to detect light (ultraviolet rays) generated from a light source 100 (a first light source), such as a flame, an LED, a lamp, or the like, an external power supply 2, a calculating device 3 to which the optical sensor 1 and the external power supply 2 are connected to each other, and an additional light source 101 (a second light source) installed such that the generated light is incident on the optical sensor 1 together with the light from the light source 100.

The optical sensor 1 is composed of a photoelectric tube including a cylindrical envelope having both end portions closed, two electrode supporting pins passing through both end portions of the envelope, and two electrodes supported in parallel with each other by the electrode supporting pins inside the envelope. In such an optical sensor 1, when one electrode disposed opposite to the light source 100 is irradiated with ultraviolet rays in a state in which a predetermined voltage is applied between the electrodes via the electrode supporting pins, electrons are emitted from the electrode by the photoelectric effect, and a discharge current flows between the electrodes.

The external power supply 2 is made of, for example, an AC commercial power supply having a voltage value of 100 [V] or 200 [V].

The calculating device 3 includes a power supply circuit 11 connected to the external power supply 2, an application voltage generating circuit 12 and a trigger circuit 13 connected to the power supply circuit 11, a voltage dividing resistor 14 constituted by resistors R1 and R2 which are connected in series between a terminal 1 b on the downstream side of the optical sensor 1 and a ground line GND, a current detecting circuit 15 configured to detect a voltage (reference voltage) Va generated at a connection point Pa between the resistors R1 and R2 of the voltage dividing resistor 14 as a current I flowing to the optical sensor 1, a processing circuit 16 to which the application voltage generating circuit 12, the trigger circuit 13, and the current detecting circuit 15 are connected, and a light source control portion 21 that controls turning-on/turning-off of the additional light source 101.

The power supply circuit 11 supplies AC power input from the external power supply 2 to the application voltage generating circuit 12 and the trigger circuit 13. Further, the power for driving the calculating device 3 is acquired from the power supply circuit 11. However, a configuration in which the power for driving is acquired from another power supply independently of AC/DC is also applicable.

The application voltage generating circuit 12 (application voltage generating portion) boosts the AC voltage applied by the power supply circuit 11 to a predetermined value to apply the voltage to the optical sensor 1. In the present embodiment, a pulse voltage (a voltage equal to or higher than a discharge starting voltage VST of the optical sensor 1) of 200 [V] synchronized with a rectangular pulse PS from the processing circuit 16 is generated as a drive pulse voltage PM, and the generated drive pulse voltage PM is applied to the optical sensor 1. FIG. 2 illustrates the drive pulse voltage PM applied to the optical sensor 1. The drive pulse voltage PM is synchronized with the rectangular pulse PS from the processing circuit 16, and a pulse width T thereof is equal to a pulse width of the rectangular pulse PS. The rectangular pulse PS from the processing circuit 16 will be described later.

The trigger circuit 13 detects a predetermined value point of the AC voltage applied by the power supply circuit 11 and inputs a result of the detection to the processing circuit 16. In the present embodiment, the trigger circuit 13 detects a minimum value point at which the voltage value is minimum as a predetermined value point (triggering time point). Detection of one cycle of the AC voltage is enabled by detecting a predetermined value point of the AC voltage in this manner.

The voltage dividing resistor 14 generates a reference voltage Va as a divided voltage of the resistors R1 and R2 and inputs the reference voltage Va to the current detecting circuit 15. Here, since a voltage value of the drive pulse PM applied to a terminal 1 a on an upstream side of the optical sensor 1 is as high as 200 [V] as described above, when a voltage generated at the terminal 1 b on the downstream side when a current flows between the electrodes of the optical sensor 1 is input to the current detecting circuit 15 as is, a large load is applied to the current detecting circuit 15. Therefore, in the present embodiment, a reference voltage Va having a low voltage value is generated by the voltage dividing resistor 14, and the reference voltage Va is input to the current detecting circuit 15.

The current detecting circuit 15 (current detecting portion) detects a reference voltage Va input from the voltage dividing resistor 14 as a discharge current I from the optical sensor 1 and inputs the detected reference voltage Va to the processing circuit 16 as a detected voltage Vpv.

The processing circuit 16 includes a rectangular pulse generating portion 17, an A/D converting portion 18, a sensitivity parameter storing portion 19, and a central processing portion 20.

The rectangular pulse generating portion 17 generates a rectangular pulse PS having a pulse width T every time when the trigger circuit 13 detects a triggering time point, that is, at every cycle of the AC voltage applied to the trigger circuit 13 from the power supply circuit 11. The rectangular pulse PS generated by the rectangular pulse generating portion 17 is sent to the application voltage generating circuit 12. The rectangular pulse generating portion 17 and the application voltage generating circuit 12 can adjust the pulse width of the drive pulse voltage PM. That is, by setting the pulse width of the rectangular pulse PS to a desired value by the rectangular pulse generating portion 17, the drive pulse voltage PM having a pulse width equal to that of the rectangular pulse PS is output from the application voltage generating circuit 12.

The A/D converting portion 18 performs A/D conversion on the detected voltage Vpv from the current detecting circuit 15 and sends the converted detected voltage Vpv to the central processing portion 20.

The central processing portion 20 is implemented by hardware constituted by a processor or a storage device and a program configured to achieve various functions in cooperation with the hardware, and functions as a discharge determining portion 201, discharge probability calculating portions 202 and 203, a number-of-times-of-pulse-application accumulating portion 204, a number-of-times-of-application determining portion 205, a received light quantity calculating portion 206, and a received light quantity determining portion 207.

In the central processing portion 20, the discharge determining portion 201 detects the discharge of the optical sensor 1 based on the discharge current from the optical sensor 1 detected by the current detecting circuit 15. Specifically, each time the drive pulse voltage PM is applied to the optical sensor 1 (each time the rectangular pulse PS is generated), the discharge determining portion 201 compares a detected voltage Vpv input from the A/D converting portion 18 with a threshold voltage Vth determined in advance (see FIG. 2), determines that the optical sensor 1 has discharged when the detected voltage Vpv exceeds the threshold voltage Vth and increments the number of times of discharge n by one.

When the number of times of application N of the drive pulse voltage PM applied to the optical sensor 1 exceeds a predetermined number (when the number of pulses of the rectangular pulse PS exceeds a predetermined number), the discharge probability calculating portion 202 calculates the discharge probability P of the optical sensor 1 based on the number of times of discharge n detected by the discharge determining portion 201 and the number of times of application N of the drive pulse voltage PM.

The discharge probability P is output as a flame signal. It is assumed that a certain operation condition, that is, a received light quantity Q₀ (Q₀≠0) and a discharge probability P₀ at a pulse width T₀ are known. For example, a shipping inspection of the light detection system includes a method of measuring the discharge probability P in predetermined received light quantity and pulse width. At this time, the relationship among the received light quantity Q, the pulse width T, and the discharge probability P is expressed by Expression (7). However, P=0 is assumed to be Q=0. In the present disclosure, cases where P=0 and P=1 are excluded from calculation processing of the received light quantity Q.

$\begin{matrix} {\frac{QT}{Q_{0}T_{0}} = {\log_{({1 - P_{0}})}\left( {1 - P} \right)}} & (7) \end{matrix}$

Now, Q₀, T₀, and P₀ are known, and T is known because T is a pulse width controlled by the light detection system. By applying the drive pulse voltages PM to the optical sensor 1 by a plurality of times, measuring the number of times of discharge n, and calculating the discharge probability P, the received light quantity Q which is an unknown number can be calculated from Expression (7). The received light quantity Q may be output as a flame signal.

[Operation of Light Detection System Taking Noise into Account]

From Expression (7), when it is assumed that a discharge probability P_(aA), in a certain operation condition, that is, with a received light quantity Q₀ and a pulse width T₀, is known, the relationship among the received light quantity Q, the pulse width T, and the discharge probability P is given by Expression (8).

$\begin{matrix} {\left( {1 - P} \right) = \left( {1 - P_{aA}} \right)^{\frac{QT}{Q_{0}T_{0}}}} & (8) \end{matrix}$

The relationship between the discharge of the optical sensor 1 and time is considered to be of two types given below.

(a) Discharge appearing at a uniform probability during an application of the drive pulse voltage PM (Expression (8)). (b) Discharge appearing at a rising edge or a falling edge of the drive pulse voltage PM.

Next, the relationship between the discharge of the optical sensor 1 and the received light quantity is considered to be of two types given below.

(A) Discharge appearing in accordance with the relationship between the received light quantity and Expression (8). (B) Discharge which appears independently of the received light quantity.

TABLE 1 Relationship between Discharge Probability and Time Discharges at a rising edge/falling Follows edge of the Expression application (8) voltage a b Relationship Follows Expression A aA bA between (8) (The discharge Discharge probability per Probability photon is constant and Light irrespective of the Quantity light quantity) Discharges B aB bB independently of the light quantity

As in the matrix in Table 1, the noise discharge of the optical sensor 1 can be classified by the combination of (a), (b) and (A), (B). In the present disclosure, it is considered that a high possibility of observation is achieved in a combination (aA) of (a) and (A), a combination (aB) of (a) and (B), a combination (bA) of (b) and (A), and a combination (bB) of (b) and (B).

The discharge of the combination of aA is called “sensitivity” and is a normal discharge (which has been incorporated into Expression (8)). The discharge of the combination of aB is a discharge that is independent of a quantity of the ultraviolet rays which may be triggered by thermal electrons or the like. The discharge of the combination of bA is a discharge that depends on the light quantity among the discharges which occur in a limited way at a rising edge or falling edge of the drive pulse voltage due to an inrush current and residual ions. The discharge of the combination of bB is a discharge that does not depend on the light quantity among discharges which occur in a limited way at a rising edge or falling edge of the drive pulse voltage due to the inrush current and the residual ions.

It should be noted that the types classified in Table are not all the UV (ultraviolet) failure modes. For example, there are failure modes not included in Table 1, such as modes in which a discharge does not end and sensitivity wavelengths are different.

The discharge of aA and the noise discharge of the three types of aB, bA, and bB can be expressed in the form of the following Expression (9).

$\begin{matrix} {\left( {1 - P} \right) = {\left( {1 - P_{aA}} \right)^{\frac{QT}{Q_{0}T_{0}}} \cdot \left( {1 - P_{aB}} \right)^{\frac{T}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)^{\frac{Q}{Q_{0}}} \cdot \left( {1 - P_{bB}} \right)}} & (9) \end{matrix}$

In Expression (9), P_(aB) is a discharge probability of aB with the received light quantity Q and the pulse width T, P_(bA) is a discharge probability of bA with the received light quantity Q and the pulse width T, and P_(bB) is a discharge probability of bB with the received light quantity Q and the pulse width T.

[Calculating Method of Discharge Probabilities P_(aA) and P_(bA)]

In Expression (9), it is assumed that the discharge probabilities P_(aA) and P_(bA) and the light quantity Q are unknown numbers, and the discharge probabilities P_(aB) and P_(bB) are known. For example, in addition to the light source 100, in a case where the received light quantity when the additional light source 101 having a known light quantity is turned on is defined as Q₁, and the received light quantity with only the light source 100 in a state where the additional light source 101 is turned off is defined as Q₂ (Q₁≠Q₂), since the difference between the received light quantities Q₁ and Q₂ is the light quantity of the additional light source 101, even when the received light quantities Q₁ and Q₂ are unknown values, Q₁−Q₂ is a known value. By using the discharge probability when the received light quantity is Q₁ as ¹P and substituting the received light quantity Q₁ and the discharge probability ¹P into Expression (9), Expression (10) is obtained.

$\begin{matrix} {\left( {1 -^{1}P} \right) = {\left( {1 - P_{aA}} \right)^{\frac{Q_{1}T}{Q_{0}T_{0}}} \cdot \left( {1 - P_{aB}} \right)^{\frac{T}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)^{\frac{Q_{1}}{Q_{0}}} \cdot \left( {1 - P_{bB}} \right)}} & (10) \end{matrix}$

Further, by using the discharge probability when the received light quantity is Q₂ as ²P and substituting the received light quantity Q₂ and the discharge probability ²P into Expression (9), Expression (11) is obtained.

$\begin{matrix} {\left( {1 -^{2}P} \right) = {\left( {1 - P_{aA}} \right)^{\frac{Q_{2}T}{Q_{0}T_{0}}} \cdot \left( {1 - P_{aB}} \right)^{\frac{T}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)^{\frac{Q_{2}}{Q_{0}}} \cdot \left( {1 - P_{bB}} \right)}} & (11) \end{matrix}$

When Expression (10) is divided by Expression (11), Expression (12) is obtained.

$\begin{matrix} {\frac{1 - {\,^{1}P}}{1 - {\,^{2}P}} = \left( {\left( {1 - P_{aA}} \right)^{\frac{T}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)} \right)^{\frac{Q_{1} - Q_{2}}{Q_{0}}}} & (12) \end{matrix}$

Further, where ¹ ₁P is the discharge probability when the pulse width of the drive pulse voltage PM is T₁ and the received light quantity is Q₁, and ² ₁P is the discharge probability when the pulse width of the drive pulse voltage PM is T₁ and the received light quantity is Q₂, Expression (13) is obtained from Expression (12).

$\begin{matrix} {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} = \left( {\left( {1 - P_{aA}} \right)^{\frac{T_{1}}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)} \right)^{\frac{Q_{1} - Q_{2}}{Q_{0}}}} & (13) \end{matrix}$

Further, where ¹ ₂P is the discharge probability when the pulse width of the drive pulse voltage PM is T₂ (T₁≠T₂) and the received light quantity is Q₁, and ² ₂P is the discharge probability when the pulse width of the drive pulse voltage PM is T₂ and the received light quantity is Q₂, Expression (14) is obtained from Expression (12).

$\begin{matrix} {\frac{1 - {\,_{2}^{1}P}}{1 - {\,_{2}^{2}P}} = \left( {\left( {1 - P_{aA}} \right)^{\frac{T_{2}}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)} \right)^{\frac{Q_{1} - Q_{2}}{Q_{0}}}} & (14) \end{matrix}$

The notations of each of the discharge probabilities when the received light quantities Q₁ and Q₂, and the pulse widths T₁ and T₂, are combined and measured, are summarized in Table 2.

TABLE 2 Light Light Quantity Q₁ Quantity Q₂ Pulse Width T₁ ¹ ₁P ² ₁P Pulse Width T₂ ¹ ₂P ² ₂P

When Expression (13) is divided by Expression (14) and modified, the discharge probability P_(aA) can be obtained as in Expression (16).

$\begin{matrix} {{\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} = \left( {1 - P_{aA}} \right)^{\frac{{({T_{1} - T_{2}})}{({Q_{1} - Q_{2}})}}{Q_{0}T_{0}}}} & (15) \\ {P_{aA} = {1 - \left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{\frac{Q_{0}T_{0}}{{({T_{1} - T_{2}})}{({Q_{1} - Q_{2}})}}}}} & (16) \end{matrix}$

Further, by substituting Expression (16) into Expression (12), the discharge probability P_(bA) can be obtained as in Expression (17).

$\begin{matrix} {{\frac{1 - {\,^{1}P}}{1 - {\,^{2}P}} = {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{\frac{T}{({T_{1} - T_{2}})}} \cdot \left( {1 - P_{bA}} \right)^{\frac{Q_{1} - Q_{2}}{Q_{0}}}}}{\left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{- \frac{T}{({T_{1} - T_{2}})}} \cdot \frac{1 - {\,^{1}P}}{1 - {\,^{2}P}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}} = {1 - P_{bA}}}{P_{bA} = {1 - \left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{- \frac{T}{({T_{1} - T_{2}})}} \cdot \frac{1 - {\,^{1}P}}{1 - {\,^{2}P}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}}}}} & (17) \end{matrix}$

Therefore, by measuring each of the discharge probabilities ¹ ₁P, ² ₁P, ¹ ₂P, ² ₂P, ¹P, and ²P, the discharge probabilities P_(aA) and P_(bA) can be obtained.

Note that T=T₁ may be set. The discharge probability P_(bA) in this case can be obtained as in Expression (18).

$\begin{matrix} {P_{bA} = {1 - \left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{- \frac{T}{({T_{1} - T_{2}})}} \cdot \frac{1 - {\,{\,_{1}^{1}P}}}{1 - {{\,_{1}^{2}P}\,}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}}}} & (18) \end{matrix}$

Further, T=T₂ may be set. The discharge probability P_(bA) in this case can be obtained as in Expression (19).

$\begin{matrix} {P_{bA} = {1 - \left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{- \frac{T}{({T_{1} - T_{2}})}} \cdot \frac{1 - {\,{\,_{2}^{1}P}}}{1 - {{\,_{2}^{2}P}\,}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}}}} & (19) \end{matrix}$

[Calculating Method of Received Light Quantity Q]

When Expression (12) is modified, Expression (20) is obtained.

$\begin{matrix} {{\left( {1 - P_{aA}} \right)^{\frac{T}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)} = \left( \frac{1 - {\,^{1}P}}{1 - {\,^{2}P}} \right)^{\frac{Q}{Q_{1} - Q_{2}}}} & (20) \end{matrix}$

As described above, T=T₁ may be set. The received light quantity Q in this case can be obtained as in Expression (21).

$\begin{matrix} {{\left( {1 - P_{aA}} \right)^{\frac{T_{1}}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)} = \left( \frac{1 - {\,{\,_{1}^{1}P}}}{1 - {\,{\,_{1}^{2}P}}} \right)^{\frac{Q}{Q_{1} - Q_{2}}}} & (21) \end{matrix}$

Further, T=T₂ may be set. The received light quantity Q in this case can be obtained as in Expression (22).

$\begin{matrix} {{\left( {1 - P_{aA}} \right)^{\frac{T_{2}}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)} = \left( \frac{1 - {\,{\,_{2}^{1}P}}}{1 - {\,{\,_{2}^{2}P}}} \right)^{\frac{Q}{Q_{1} - Q_{2}}}} & (22) \end{matrix}$

As described above, when the discharge probabilities P_(aA) and P_(bA) are known from Expressions (16) to (19), the received light quantity Q can be obtained by using Expressions (20) to (22).

Therefore, even when at least one of the discharge probabilities P_(aB) and P_(bB) is an unknown number, by using an additional light source 101 having a known light quantity in addition to the light source 100 to be detected, the received light quantity Q can be obtained.

Hereinafter, an operation of the light detection system of the present embodiment will be described in more detail. FIGS. 3 and 4 are flowcharts explaining the operation of the light detection system according to the present embodiment.

First, the discharge probability calculating portion 202 initializes a variable i for a pulse width control to 1 (step S100 in FIG. 3). The discharge probability calculating portion 202 instructs the light source control portion 21 to turn on the additional light source 101.

In response to an instruction from the discharge probability calculating portion 202, the light source control portion 21 turns on the additional light source 101 (step S101 in FIG. 3). The received light quantity received by the optical sensor 1 at this time is an unknown value Q₁. The additional light source 101 includes, for example, an LED.

When the variable i is smaller than 3 (YES in step S102 in FIG. 3), the discharge probability calculating portion 202 instructs the rectangular pulse generating portion 17 to start an application of the drive pulse voltage PM. In response to the instruction from the discharge probability calculating portion 202, the rectangular pulse generating portion 17 sets the pulse width of the rectangular pulse PS to a predetermined value T_(i)=T₁. By setting the pulse width, the application voltage generating circuit 12 applies the drive pulse voltage PM having the pulse width T_(i)=T₁ between a pair of terminals 1 a and 1 b of the optical sensor 1 (step S103 in FIG. 3).

The discharge determining portion 201 compares the detected voltage Vpv from the current detecting circuit 15 with a threshold voltage Vth determined in advance and determines that the optical sensor 1 discharges when the detected voltage Vpv exceeds the threshold voltage Vth. When it is determined that the optical sensor 1 discharges, the discharge determining portion 201 counts the number of times of discharge ¹ _(i)n=¹ ₁n with the discharge as one time (step S104 in FIG. 3). Needless to say, an initial value of the number of times of discharge ¹ ₁n and an initial value of the number of times of application ¹ ₁N of the drive pulse voltage PM to be described later are both 0. In this manner, the processes in steps S103 and S104 are repeatedly executed.

The number-of-times-of-pulse-application accumulating portion 204 counts the rectangular pulse PS output from the rectangular pulse generating portion 17 to count the number of times of application ¹ _(i)N of the drive pulse voltage PM.

The number-of-times-of-application determining portion 205 compares the number of times of application of the drive pulse voltage PM with a predetermined number Nth.

When the number-of-times-of-application determining portion 205 determines that the number of times of application ¹ _(i)N=¹ ₁N of the drive pulse voltage PM from the start of application of the drive pulse voltage PM having a pulse width T_(i)=T₁ in step S103 exceeds the predetermined number Nth (YES in step S105 in FIG. 3), the discharge probability calculating portion 202 calculates the discharge probability ¹ ₁P based on the number of times of application ¹ _(i)N=¹ ₁N of the drive pulse voltage PM at this time and the number of times of discharge ¹ _(i)n=¹ ₁n detected by the discharge determining portion 201 by Expression (23) (step S106 in FIG. 3).

¹ ₁ P= ¹ ₁ n/ ¹ ₁ N  (23)

After the discharge probability ¹ ₁P is calculated, the discharge probability calculating portion 202 increments the variable i for a pulse width control by 1 (step S107 in FIG. 3). When the variable i is smaller than 3 (YES in step S102), the discharge probability calculating portion 202 instructs the rectangular pulse generating portion 17 to start the application of the drive pulse voltage PM again.

In response to the instruction from the discharge probability calculating portion 202, the rectangular pulse generating portion 17 temporarily stops the output of the rectangular pulse PS, and then sets the pulse width of the rectangular pulse PS to a predetermined value T_(i)=T₂ (T₁≠T₂). By setting the pulse width, the application voltage generating circuit 12 applies the drive pulse voltage PM having the pulse width T_(i)=T₂ between a pair of terminals 1 a and 1 b of the optical sensor 1 (step S103).

The discharge determining portion 201 compares the detected voltage Vpv from the current detecting circuit 15 with the threshold voltage Vth the same as above, determines that the optical sensor 1 discharges when the detected voltage Vpv exceeds the threshold voltage Vth, and increments the number of times of discharge ¹ _(i)n=¹ ₂n by one (step S104). An initial value of the number of times of discharge ¹ ₂n and an initial value of the number of times of application ¹ ₂N of the drive pulse voltage PM to be described later are both 0. In this manner, the processes in steps S103 and S104 are repeatedly executed.

When the number-of-times-of-application determining portion 205 determines that the number of times of application ¹ _(i)N=¹ ₂N of the drive pulse voltage PM from the start of application of the drive pulse voltage PM having a pulse width T_(i)=T₂ in step S103 exceeds the predetermined number Nth (YES in step S105), the discharge probability calculating portion 202 calculates the discharge probability ¹ ₂P based on the number of times of application ¹ _(i)N=¹ ₂N of the drive pulse voltage PM at this time and the number of times of discharge ¹ _(i)n=¹ ₂n detected by the discharge determining portion 201 by Expression (24) (step S106).

¹ ₂ P= ¹ ₂ n/ ¹ ₂ N  (24)

After the discharge probability ¹ ₂P is calculated, the discharge probability calculating portion 202 increments the variable i for a pulse width control by 1 (step S107). In a case where the measurement of the received light quantity Q₁ is ended, that is, in a case where the variable i reaches (NO in step S102), the discharge probability calculating portion 202 initializes the variable i to 1 (step S108 in FIG. 3). Thereafter, the discharge probability calculating portion 202 instructs the light source control portion 21 to turn off the additional light source 101.

In response to an instruction from the discharge probability calculating portion 202, the light source control portion 21 turns off the additional light source 101 (step S109 in FIG. 3). The received light quantity received by the optical sensor 1 at this time is an unknown value Q₂. As described above, Q₁−Q₂ is a known value.

When the variable i is smaller than 3 (YES in step S110 in FIG. 3), the discharge probability calculating portion 202 instructs the rectangular pulse generating portion 17 to start an application of the drive pulse voltage PM. In response to the instruction from the discharge probability calculating portion 202, the rectangular pulse generating portion 17 sets the pulse width of the rectangular pulse PS to a predetermined value T_(i)=T₁. By setting the pulse width, the application voltage generating circuit 12 applies the drive pulse voltage PM having the pulse width T_(i)=T₁ between a pair of terminals 1 a and 1 b of the optical sensor 1 (step S111 in FIG. 3).

The discharge determining portion 201 compares the detected voltage Vpv from the current detecting circuit 15 with the threshold voltage Vth the same as above, determines that the optical sensor 1 discharges when the detected voltage Vpv exceeds the threshold voltage Vth, and increments the number of times of discharge ² _(i)n=² _(i)n by one (step S112). An initial value of the number of times of discharge ² ₁n and an initial value of the number of times of application ² ₁N of the drive pulse voltage PM to be described later are both 0. In this manner, the processes in steps S111 and S112 are repeatedly executed.

When the number-of-times-of-application determining portion 205 determines that the number of times of application ² _(i)N=² ₁N of the drive pulse voltage PM from the start of application of the drive pulse voltage PM having a pulse width T_(i)=T₁ in step S111 exceeds the predetermined number Nth (YES in step S113 in FIG. 3), the discharge probability calculating portion 202 calculates the discharge probability ² ₁P based on the number of times of application ² _(i)N=² ₁N of the drive pulse voltage PM at this time and the number of times of discharge ² _(i)n=² ₁n detected by the discharge determining portion 201 by Expression (25) (step S114 in FIG. 3).

² ₁ P= ² ₁ n/ ² ₁ N  (25)

After the discharge probability ² ₁P is calculated, the discharge probability calculating portion 202 increments the variable i for a pulse width control by 1 (step S115 in FIG. 3). When the variable i is smaller than 3 (YES in step S110), the discharge probability calculating portion 202 instructs the rectangular pulse generating portion 17 to start the application of the drive pulse voltage PM again.

In response to the instruction from the discharge probability calculating portion 202, the rectangular pulse generating portion 17 temporarily stops the output of the rectangular pulse PS, and then sets the pulse width of the rectangular pulse PS to a predetermined value T_(i)=T₂ (T₁≠T₂). By setting the pulse width, the application voltage generating circuit 12 applies the drive pulse voltage PM having the pulse width T₁=T₂ between a pair of terminals 1 a and 1 b of the optical sensor 1 (step S111).

The discharge determining portion 201 compares the detected voltage Vpv from the current detecting circuit 15 with the threshold voltage Vth the same as above, determines that the optical sensor 1 discharges when the detected voltage Vpv exceeds the threshold voltage Vth, and increments the number of times of discharge ² _(i)n=² ₂n by one (step S112). An initial value of the number of times of discharge ² ₂n and an initial value of the number of times of application ² ₂N of the drive pulse voltage PM to be described later are both 0. In this manner, the processes in steps S111 and S112 are repeatedly executed.

When the number-of-times-of-application determining portion 205 determines that the number of times of application ² _(i)N=² ₂N of the drive pulse voltage PM from the start of application of the drive pulse voltage PM having a pulse width T_(i)=T₂ in step S111 exceeds the predetermined number Nth (YES in step S113), the discharge probability calculating portion 202 calculates the discharge probability ² ₂P based on the number of times of application ² _(i)N=² ₂N of the drive pulse voltage PM at this time and the number of times of discharge ² _(i)n=² ₂n detected by the discharge determining portion 201 by Expression (26) (step S114).

² ₂ P= ² ₂ n/ ² ₂ N  (26)

After the discharge probability ² ₂P is calculated, the discharge probability calculating portion 202 increments the variable i for a pulse width control by 1 (step S115). In a case where the measurement of the received light quantity Q₂ is ended, that is, in a case where the variable i reaches (NO in step S110), the discharge probability calculating portion 202 instructs the light source control portion 21 to turn on the additional light source 101, and then instructs the rectangular pulse generating portion 17 to start the application of the drive pulse voltage PM.

In response to an instruction from the discharge probability calculating portion 202, the light source control portion 21 turns on the additional light source 101 (step S116 in FIG. 3). The received light quantity received by the optical sensor 1 at this time is Q₁.

In response to the instruction from the discharge probability calculating portion 202, the rectangular pulse generating portion 17 sets the pulse width of the rectangular pulse PS to a predetermined value T. By setting the pulse width, the application voltage generating circuit 12 applies the drive pulse voltage PM having the pulse width T between a pair of terminals 1 a and 1 b of the optical sensor 1 (step S117 in FIG. 3).

The discharge determining portion 201 compares the detected voltage Vpv from the current detecting circuit 15 with the threshold voltage Vth the same as above, determines that the optical sensor 1 discharges when the detected voltage Vpv exceeds the threshold voltage Vth, and increments the number of times of discharge n₁ by one (step S118 in FIG. 3). An initial value of the number of times of discharge n₁ and an initial value of the number of times of application N₁ of the drive pulse voltage PM to be described later are both 0. In this manner, the processes in steps S117 and S118 are repeatedly executed.

When the number-of-times-of-application determining portion 205 determines that the number of times of application N₁ of the drive pulse voltage PM from the start of application of the drive pulse voltage PM in step S117 exceeds the predetermined number Nth (YES in step S119 in FIG. 3), the discharge probability calculating portion 202 calculates the discharge probability ¹P based on the number of times of application N₁ of the drive pulse voltage PM at this time and the number of times of discharge n₁ detected by the discharge determining portion 201 by Expression (27) (step S120 in FIG. 3).

¹ P=n ₁ /N ₁  (27)

After the discharge probability ¹P is calculated, the discharge probability calculating portion 202 instructs the light source control portion 21 to turn off the additional light source 101 and then instructs the rectangular pulse generating portion 17 to start applying the drive pulse voltage PM. In response to an instruction from the discharge probability calculating portion 202, the light source control portion 21 turns off the additional light source 101 (step S121 in FIG. 3). The received light quantity received by the optical sensor 1 at this time is Q₂.

In response to the instruction from the discharge probability calculating portion 202, the rectangular pulse generating portion 17 temporarily stops the output of the rectangular pulse PS, and then sets the pulse width of the rectangular pulse PS again to a predetermined value T. By setting the pulse width, the application voltage generating circuit 12 applies the drive pulse voltage PM having the pulse width T between a pair of terminals 1 a and 1 b of the optical sensor 1 (step S122 in FIG. 3).

The discharge determining portion 201 compares the detected voltage Vpv from the current detecting circuit 15 with the threshold voltage Vth the same as above, determines that the optical sensor 1 discharges when the detected voltage Vpv exceeds the threshold voltage Vth, and increments the number of times of discharge n₂ by one (step S123 in FIG. 3). An initial value of the number of times of discharge n₂ and an initial value of the number of times of application N₂ of the drive pulse voltage PM to be described later are both 0. In this manner, the processes in steps S122 and S123 are repeatedly executed.

When the number-of-times-of-application determining portion 205 determines that the number of times of application N₂ of the drive pulse voltage PM from the start of application of the drive pulse voltage PM in step S122 exceeds the predetermined number Nth (YES in step S124 in FIG. 3), the discharge probability calculating portion 202 calculates the discharge probability ²P based on the number of times of application N₂ of the drive pulse voltage PM at this time and the number of times of discharge n₂ detected by the discharge determining portion 201 by Expression (28) (step S125 in FIG. 3).

² P=n ₂ /N ₂  (28)

A sensitivity parameter storing portion 19 stores, in advance as known sensitivity parameters of the optical sensor 1, a reference received light quantity Q₀ received by the optical sensor 1, a reference pulse width T₀ of the drive pulse voltage PM, and the difference Q₁−Q₂ between the received light quantities when the additional light source 101 is turned on and turned off.

It is assumed that a sensitivity parameter stored in the sensitivity parameter storing portion 19 is measured in advance, for example, in the shipping inspection of the light detection system.

After the discharge probability ²P is calculated, based on the discharge probabilities ¹ ₁P, ² ₁P, ¹ ₂P, and ² ₂P calculated by the discharge probability calculating portion 202, the pulse width T₁ of the drive pulse voltage PM when the discharge probabilities ¹ ₁P and ² ₁P are obtained, the pulse width T₂ of the drive pulse voltage PM when the discharge probabilities ¹ ₂P and ² ₂P are obtained, and the parameters T₀, Q₀, and Q₁−Q₂ stored in the sensitivity parameter storing portion 19, the discharge probability calculating portion 203 calculates the discharge probability P_(aA) by using Expression (16) (step S126 in FIG. 3). As described above, the discharge probability P_(aA) is a discharge probability of a regular discharge when the pulse width of the drive pulse voltage PM is the reference pulse width T₀ and the received light quantity received by the optical sensor 1 is the reference received light quantity Q₀.

Further, based on the discharge probabilities ¹ ₁P, ² ₁P, ¹ ₂P, ² ₂P, ¹P, and ²P calculated by the discharge probability calculating portion 202, the pulse width T₁ of the drive pulse voltage PM when the discharge probabilities ¹ ₁P and ² ₁P are obtained, the pulse width T₂ of the drive pulse voltage PM when the discharge probabilities ¹ ₂P and ² ₂P are obtained, the pulse width T of the drive pulse voltage PM when the discharge probabilities ¹P and ²P are obtained, and the parameters Q₀ and Q₁−Q₂ stored in the sensitivity parameter storing portion 19, the discharge probability calculating portion 203 calculates the discharge probability P_(bA) by using Expression (17) (step S127 in FIG. 3). The discharge probability P_(bA) is a probability of a discharge caused by the noise component other than a discharge occurring due to a photoelectric effect of the optical sensor 1 which occurs without depending on the pulse width of the drive pulse voltage PM and occurs depending on the received light quantity received by the optical sensor 1 as described above.

When the discharge probabilities P_(aA) and P_(bA) calculated by the discharge probability calculating portion 203 are greater than 0 and less than 1 (YES in step S128 in FIG. 4), based on the discharge probabilities ¹P and ²P calculated by the discharge probability calculating portion 202, the pulse width T of the drive pulse voltage PM when the discharge probabilities ¹P and ²P are obtained, the discharge probabilities P_(aA) and P_(bA) calculated by the discharge probability calculating portion 203, and the parameters T₀ and Q₁−Q₂ stored in the sensitivity parameter storing portion 19, the received light quantity calculating portion 206 calculates the received light quantity Q by using Expression (20) (step S129 in FIG. 4).

Further, when at least one of the discharge probabilities P_(aA) and P_(bA) is 0 (NO in step S128), the received light quantity calculating portion 206 performs exception processing which sets the received light quantity Q to 0 or disables calculation of the received light quantity Q (step S130 in FIG. 4). Further, when at least one of the discharge probabilities P_(aA) and P_(bA) is 1 (NO in step S128), the received light quantity calculating portion 206 performs the exception processing which disables the calculation of the received light quantity Q (step S130).

Next, the received light quantity determining portion 207 compares the received light quantity Q calculated by the received light quantity calculating portion 206 with a predetermined received light quantity threshold value Qth (step S131 in FIG. 4), and when the received light quantity Q exceeds the received light quantity threshold value Qth (YES in step S131), determines that a flame exists (step S132 in FIG. 4). Further, when the received light quantity Q is equal to or less than the received light quantity threshold value Qth (NO in Step S131), the received light quantity determining portion 207 determines that a flame does not exist (Step S133 in FIG. 4).

As can be seen from the above description, in the present embodiment, it is possible to calculate the discharge probability P_(aA) of the regular discharge excluding a noise component and the discharge probability P_(bA) of the irregular discharge that occurs without depending on the pulse width of the drive pulse voltage PM and occurs depending on the received light quantity received by the optical sensor 1. As it is considered that the discharge probabilities P_(aA) and P_(bA) are changed with the degradation of the optical sensor 1, it is possible to implement a life determination of the optical sensor 1 based on the discharge probabilities P_(aA) and P_(bA).

Further, in the present embodiment, even when at least one of the discharge probabilities P_(aB) and P_(bB) is an unknown number, the received light quantity Q can be calculated, and it is thereby possible to accurately detect the presence or absence of a flame by using the obtained received light quantity Q. Further, in the present embodiment, it is possible to reduce the possibility that the life of the optical sensor 1 is erroneously determined by using the received light quantity Q.

In the present embodiment, T≠T₁≠T₂ may be set, or T=T₁ or T=T₂ may be set. When T=T₁, the processes illustrated in FIGS. 5 and 6 can be performed instead of the processes illustrated in FIGS. 3 and 4. The processes of steps S100 to S115 in FIG. 5 are as described with reference to FIG. 3.

In a case where the measurement of the received light quantity Q₂ is ended, that is, in a case where the variable i reaches 3 (NO in step S110 in FIG. 5), the discharge probability calculating portion 203 calculates the discharge probability P_(aA) by using Expression (16) (step S126 in FIG. 5).

Further, based on the discharge probabilities ¹ ₁P, ² ₁P, ¹ ₂P, and ² ₂P calculated by the discharge probability calculating portion 202, the pulse width T₁ of the drive pulse voltage PM when the discharge probabilities ¹ ₁P and ² ₁P are obtained, the pulse width T₂ of the drive pulse voltage PM when the discharge probabilities ¹ ₂P and ² ₂P are obtained, and the parameters Q₀ and Q₁−Q₂ stored in the sensitivity parameter storing portion 19, the discharge probability calculating portion 203 calculates the discharge probability P_(bA) by using Expression (18) (step S127 a in FIG. 5).

The processes of steps S128 and S130 to S133 in FIG. 6 are as described with reference to FIG. 4. When the discharge probabilities P_(aA) and P_(bA) calculated by the discharge probability calculating portion 203 are greater than 0 and less than 1 (YES in step S128 in FIG. 6), based on the discharge probabilities ¹ ₁P and ² ₁P calculated by the discharge probability calculating portion 202, the pulse width T₁ of the drive pulse voltage PM when the discharge probabilities ¹ ₁P and ² ₁P are obtained, the discharge probabilities P_(aA) and P_(bA) calculated by the discharge probability calculating portion 203, and the parameters T₀ and Q₁−Q₂ stored in the sensitivity parameter storing portion 19, the received light quantity calculating portion 206 calculates the received light quantity Q by using Expression (21) (step S129 a in FIG. 6).

The case of T=T₂ is the same as the case of T=T₁. When T=T₂, the discharge probability calculating portion 203 may calculate the discharge probability P_(bA) by using Expression (19) in step S127 a in FIG. 5. When T=T₂, the received light quantity calculating portion 206 may calculate the received light quantity Q by using Expression (22) in step S129 a in FIG. 6. Other processes are the same as in the case of T=T₁.

In the present embodiment, a state in which the additional light source 101 is turned on is defined as a first state (pulse width T₁), a second state (pulse width T₂), and a fifth state (pulse width T), a state in which the additional light source 101 is turned off is defined as a third state (pulse width T₁), a fourth state (pulse width T₂), and a sixth state (pulse width T), and Q₁−Q₂ is defined as a positive value (Q₁>Q₂), but Q₁−Q₂ may be defined as a negative value (Q₁<Q₂).

Specifically, the discharge probability calculating portion 202 may turn off the additional light source 101 in steps S101 and S116 in FIGS. 3 and 5 and turn on the additional light source 101 in steps S109 and S121 in FIGS. 3 and 5. As a result, a state in which the additional light source 101 is turned off and the pulse width is T₁ is the first state, a state in which the additional light source 101 is turned off and the pulse width is T₂ is the second state, a state in which the additional light source 101 is turned off and the pulse width is T is the fifth state, a state in which the additional light source 101 is turned on and the pulse width is T₁ is the third state, a state in which the additional light source 101 is turned on and the pulse width is T₂ is the fourth state, and a state in which the additional light source 101 is turned on and the pulse width is T is the sixth state.

However, when the additional light source 101 is turned on in step S121 in FIG. 3, after the discharge probability ²P is calculated, the discharge probability calculating portion 202 needs to instruct the light source control portion 21 to turn off the additional light source 101. Further, when the additional light source 101 is turned on in step S109 in FIG. 5, after the variable i reaches 3 in step S110, the discharge probability calculating portion 202 needs to instruct the light source control portion 21 to turn off the additional light source 101.

Second Embodiment

Next, a second embodiment of the present disclosure will be described. FIG. 7 is a block diagram illustrating a configuration of a light detection system according to the second embodiment of the present disclosure, and the same configuration as that in FIG. 1 is designated by the same reference numerals. The light detection system of the present embodiment includes an optical sensor 1, an external power supply 2, a calculating device 3 a, and an additional light source 101.

The calculating device 3 a includes a power supply circuit 11, an application voltage generating circuit 12, a trigger circuit 13, a voltage dividing resistor 14, a current detecting circuit 15, a processing circuit 16 a, and a light source control portion 21.

The processing circuit 16 a includes a rectangular pulse generating portion 17 a, an A/D converting portion 18, a sensitivity parameter storing portion 19, and a central processing portion 20 a.

The central processing portion 20 a functions as a discharge determining portion 201, discharge probability calculating portions 202 a and 203 a, a number-of-times-of-pulse-application accumulating portion 204, a number-of-times-of-application determining portion 205, a received light quantity calculating portion 206, and a received light quantity determining portion 207.

[Calculating Method of Discharge Probabilities P_(aA) and P_(bA)]

Further, when the pulse width T₁, the received light quantity Q₁, and the discharge probability ¹ ₁P are substituted into Expression (9), where the pulse width of the drive pulse voltage PM is T₁ and the discharge probability when the received light quantity is Q₁ is ¹ ₁P, Expression (29) is obtained.

$\begin{matrix} {\left( {1 - {\,_{1}^{1}P}} \right) = {\left( {1 - P_{aA}} \right)^{\frac{Q_{1}T_{1}}{Q_{0}T_{0}}} \cdot \left( {1 - P_{aB}} \right)^{\frac{T_{1}}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)^{\frac{Q_{1}}{Q_{0}}} \cdot \left( {1 - P_{bB}} \right)}} & (29) \end{matrix}$

Further, when the pulse width T₂, the received light quantity Q₁, and the discharge probability ¹ ₂P are substituted into Expression (9), where the pulse width of the drive pulse voltage PM is T₂ (T₁≠T₂) and the discharge probability when the received light quantity is Q₁ is ¹ ₂P, Expression (30) is obtained.

$\begin{matrix} {\left( {1 - {\,_{2}^{1}P}} \right) = {\left( {1 - P_{aA}} \right)^{\frac{Q_{1}T_{2}}{Q_{0}T_{0}}} \cdot \left( {1 - P_{aB}} \right)^{\frac{T_{2}}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)^{\frac{Q_{1}}{Q_{0}}} \cdot \left( {1 - P_{bB}} \right)}} & (30) \end{matrix}$

When the pulse width T₃, the received light quantity Q₂, and the discharge probability ² ₃P are substituted into Expression (9), where the pulse width of the drive pulse voltage PM is T₃ and the discharge probability when the received light quantity is Q₂ is ² ₃P, Expression (31) is obtained.

$\begin{matrix} {\left( {1 - {\,_{3}^{2}P}} \right) = {\left( {1 - P_{aA}} \right)^{\frac{Q_{2}T_{3}}{Q_{0}T_{0}}} \cdot \left( {1 - P_{aB}} \right)^{\frac{T_{3}}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)^{\frac{Q_{2}}{Q_{0}}} \cdot \left( {1 - P_{bB}} \right)}} & (31) \end{matrix}$

When the pulse width T₄, the received light quantity Q₂, and the discharge probability ² ₄P are substituted into Expression (9), where the pulse width of the drive pulse voltage PM is T₄ (T₃≠T₄) and the discharge probability when the received light quantity is Q₂ is ² ₄P, Expression (32) is obtained.

$\begin{matrix} {\left( {1 - {\,_{4}^{2}P}} \right) = {\left( {1 - P_{aA}} \right)^{\frac{Q_{2}T_{4}}{Q_{0}T_{0}}} \cdot \left( {1 - P_{aB}} \right)^{\frac{T_{4}}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)^{\frac{Q_{2}}{Q_{0}}} \cdot \left( {1 - P_{bB}} \right)}} & (32) \end{matrix}$

The notations of each of the discharge probabilities when the received light quantities Q₁ and Q₂, and the pulse widths T₁, T₂, T₃, and T₄, are combined and measured, are summarized in Table 3.

TABLE 3 Light Light Quantity Q₁ Quantity Q₂ Pulse Width T₁ ¹ ¹ P — Pulse Width T₂ ¹ ² P — Pulse Width T₃ — ² ³ P Pulse Width T₄ — ² ⁴ P

When Expression (29) is divided by Expression (30), Expression (33) is obtained.

$\begin{matrix} {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} = \left( {\left( {1 - P_{aA}} \right)^{\frac{Q_{1}}{Q_{0}}} \cdot \left( {1 - P_{aB}} \right)} \right)^{\frac{T_{1} - T_{2}}{T_{0}}}} & (33) \end{matrix}$

When Expression (31) is divided by Expression (32), Expression (34) is obtained.

$\begin{matrix} {\frac{1 - {\,_{3}^{2}P}}{1 - {\,_{4}^{2}P}} = \left( {\left( {1 - P_{aA}} \right)^{\frac{Q_{2}}{Q_{0}}} \cdot \left( {1 - P_{aB}} \right)} \right)^{\frac{T_{3} - T_{4}}{T_{0}}}} & (34) \end{matrix}$

When Expression (33) is divided by Expression (34), Expression (35) is obtained.

$\begin{matrix} {{\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} = {\left( {1 - P_{aA}} \right)^{\frac{{Q_{1}{({T_{1} - T_{2}})}} - {Q_{2}{({T_{3} - T_{4}})}}}{Q_{0}}} \cdot \left( {1 - P_{aB}} \right)^{\frac{{({T_{1} - T_{2}})} - {({T_{3} - T_{4}})}}{T_{0}}}}} & (35) \end{matrix}$

In a case where T₁−T₂=T₃−T₄, when Expression (35) is modified, the discharge probability P_(aA) can be obtained as in Expression (36). Here, T₁=T₃ and T₂=T₄ may be set, or T₁≠T₃ and T₂≠T₄ may be set.

$\begin{matrix} {{{\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} = {\left( {1 - P_{aA}} \right)^{\frac{{Q_{1}{({T_{1} - T_{2}})}} - {Q_{2}{({T_{1} - T_{2}})}}}{Q_{0}}} \cdot \left( {1 - P_{aB}} \right)^{\frac{{({T_{1} - T_{2}})} - {({T_{1} - T_{2}})}}{T_{0}}}}}\mspace{76mu}{{\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} = \left( {1 - P_{aA}} \right)^{\frac{{({Q_{1} - Q_{2}})}{({T_{1} - T_{2}})}}{Q_{0}}}}\mspace{76mu}{P_{aA} = {1 - \left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} \right)^{\frac{Q_{0}}{{({Q_{1} - Q_{2}})}{({T_{1} - T_{2}})}}}}}} & (36) \end{matrix}$

Further, by substituting Expression (36) into Expression (12), the discharge probability P_(bA) can be obtained as in Expression (37).

$\begin{matrix} {{\frac{1 - {\,^{1}P}}{{\, 1} - {\,^{2}P}} = {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} \right)^{\frac{T}{{({T_{1} - T_{2}})}T_{0}}} \cdot \left( {1 - P_{bA}} \right)^{\frac{Q_{1} - Q_{2}}{Q_{0}}}}}{\left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} \right)^{- \frac{T}{{({T_{1} - T_{2}})}T_{0}}} \cdot \frac{1 - {\,^{1}P}}{{\, 1} - {\,^{2}P}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}} = {1 - P_{bA}}}{P_{bA} = {1 - \left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} \right)^{- \frac{T}{{({T_{1} - T_{2}})}T_{0}}} \cdot \frac{1 - {\,^{1}P}}{{\, 1} - {\,^{2}P}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}}}}} & (37) \end{matrix}$

Hereinafter, an operation of the light detection system of the present embodiment will be described in more detail. FIG. 8 is a flowchart explaining an operation of the light detection system according to the present embodiment. The processes of steps S100 to S107 in FIG. 8 are the same as those of the first embodiment.

In a case where the measurement of the received light quantity Q₁ is ended, that is, in a case where the variable i reaches 3 (NO in step S102), the discharge probability calculating portion 202 a instructs the light source control portion 21 to turn off the additional light source 101.

In response to an instruction from the discharge probability calculating portion 202 a, the light source control portion 21 turns off the additional light source 101 (step S109 in FIG. 8). The received light quantity received by the optical sensor 1 at this time is an unknown value Q₂. As described in the first embodiment, Q₁−Q₂ is a known value.

When the variable i is smaller than 5 (YES in step S110 b in FIG. 8), the discharge probability calculating portion 202 a instructs the rectangular pulse generating portion 17 a to start an application of the drive pulse voltage PM. In response to the instruction from the discharge probability calculating portion 202 a, the rectangular pulse generating portion 17 a sets the pulse width of the rectangular pulse PS to a predetermined value T_(i)=T₃. By setting the pulse width, the application voltage generating circuit 12 applies the drive pulse voltage PM having the pulse width T_(i)=T₃ between a pair of terminals 1 a and 1 b of the optical sensor 1 (step S111 b in FIG. 8).

Same as above, the discharge determining portion 201 determines that the optical sensor 1 discharges when the detected voltage Vpv from the current detecting circuit 15 exceeds the threshold voltage Vth and increments the number of times of discharge ² _(i)n=² ₃n by one (step S112 b in FIG. 8). An initial value of the number of times of discharge ² ₃n and an initial value of the number of times of application ² ₃N of the drive pulse voltage PM to be described later are both 0. In this manner, the processes in steps S111 b and S112 b are repeatedly executed.

When the number-of-times-of-application determining portion 205 determines that the number of times of application ² _(i)N=² ₃N of the drive pulse voltage PM from the start of application of the drive pulse voltage PM having a pulse width T_(i)=T₃ in step S111 b exceeds the predetermined number Nth (YES in step S113 b in FIG. 8), the discharge probability calculating portion 202 a calculates the discharge probability ² ₃P based on the number of times of application ² _(i)N=² ₃N of the drive pulse voltage PM at this time and the number of times of discharge ² _(i)n=² ₃n detected by the discharge determining portion 201 by Expression (38) (step S114 b in FIG. 8).

2₃ P= ² ₃ n/ ² ₃ N  (38)

After the discharge probability ² ₃P is calculated, the discharge probability calculating portion 202 a increments the variable i for a pulse width control by 1 (step S115 in FIG. 8). When the variable i is smaller than 5 (YES in step S110 b), the discharge probability calculating portion 202 a instructs the rectangular pulse generating portion 17 a to start an application of the drive pulse voltage PM again.

In response to the instruction from the discharge probability calculating portion 202 a, the rectangular pulse generating portion 17 a temporarily stops the output of the rectangular pulse PS, and then sets the pulse width of the rectangular pulse PS to a predetermined value T_(i)=T₄ (T₃≠T₄). By setting the pulse width, the application voltage generating circuit 12 applies the drive pulse voltage PM having the pulse width T_(i)=T₄ between a pair of terminals 1 a and 1 b of the optical sensor 1 (step S111 b).

The discharge determining portion 201 determines that the optical sensor 1 discharges when the detected voltage Vpv from the current detecting circuit 15 exceeds the threshold voltage Vth and increments the number of times of discharge ² _(i)n=² ₄n by one (step S112 b). An initial value of the number of times of discharge ² ₄n and an initial value of the number of times of application ² ₄N of the drive pulse voltage PM to be described later are both 0. In this manner, the processes in steps S111 b and S112 b are repeatedly executed.

When the number-of-times-of-application determining portion 205 determines that the number of times of application ² _(i)N=² ₄N of the drive pulse voltage PM from the start of application of the drive pulse voltage PM having a pulse width T_(i)=T₄ in step S111 b exceeds the predetermined number Nth (YES in step S113 b), the discharge probability calculating portion 202 a calculates the discharge probability ² ₄P based on the number of times of application ² _(i)N=² ₄N of the drive pulse voltage PM at this time and the number of times of discharge ² _(i)n=² ₄n detected by the discharge determining portion 201 by Expression (39) (step S114 b).

2₄ P=2₄ n/ ² ₄ N  (39)

After the discharge probability ² ₄P is calculated, the discharge probability calculating portion 202 a increments the variable i for a pulse width control by 1 (step S115). In a case where the measurement of the received light quantity Q₂ is ended, that is, in a case where the variable i reaches 5 (NO in step S110 b), the discharge probability calculating portion 202 a instructs the light source control portion 21 to turn on the additional light source 101, and then instructs the rectangular pulse generating portion 17 a to start the application of the drive pulse voltage PM.

In response to an instruction from the discharge probability calculating portion 202 a, the light source control portion 21 turns on the additional light source 101 (step S116 in FIG. 8). The received light quantity received by the optical sensor 1 at this time is Q₁. The processes of steps S117 to S125 in FIG. 8 are the same as those of the first embodiment.

After the discharge probability ²P is calculated, based on the discharge probabilities ¹ ₁P, ¹ ₂P, ² ₃P, and ² ₄P calculated by the discharge probability calculating portion 202 a, the pulse width T₁ of the drive pulse voltage PM when the discharge probability ¹ ₁P is obtained, the pulse width of the drive pulse voltage PM when the discharge probability ¹ ₂P is obtained, and the parameters Q₀ and Q₁−Q₂ stored in the sensitivity parameter storing portion 19, the discharge probability calculating portion 203 a calculates the discharge probability P_(aA) by using Expression (36) (step S126 b in FIG. 8).

Further, based on the discharge probabilities ¹ ₁P, ¹ ₂P, ² ₃P, ² ₄P, ¹P, and ²P calculated by the discharge probability calculating portion 202 a, the pulse width T₁ of the drive pulse voltage PM when the discharge probability ¹ ₁P is obtained, the pulse width T₂ of the drive pulse voltage PM when the discharge probability ¹ ₂P is obtained, the pulse width T of the drive pulse voltage PM when the discharge probabilities ¹P and ²P are obtained, and the parameters Q₀, T₀, and Q₁−Q₂ stored in the sensitivity parameter storing portion 19, the discharge probability calculating portion 203 a calculates the discharge probability P_(bA) by using Expression (37) (step S127 b in FIG. 8).

Since the processes after step S128 are as described with reference to FIG. 4, the illustration is omitted.

In this way, in the present embodiment, the same effect as in the first embodiment can be obtained. In the present embodiment, the discharge probabilities P_(aA) and P_(bA) and the received light quantity Q are calculated, but when only the discharge probabilities P_(aA) and P_(bA) are calculated, the received light quantity calculating portion 206, the received light quantity determining portion 207, and the processes after step S128 are unnecessary.

Further, in the present embodiment, a state in which the additional light source 101 is turned on is defined as a first state (pulse width T₁), a second state (pulse width T₂), and a fifth state (pulse width T), a state in which the additional light source 101 is turned off is defined as a third state (pulse width T₃), a fourth state (pulse width T₄), and a sixth state (pulse width T), and Q₁−Q₂ is defined as a positive value (Q₁>Q₂), but Q₁−Q₂ may be defined as a negative value (Q₁<Q₂).

Specifically, the discharge probability calculating portion 202 a may turn off the additional light source 101 in steps S101 and S116 in FIG. 8 and turn on the additional light source 101 in steps S109 and S121 in FIG. 8. As a result, a state in which the additional light source 101 is turned off and the pulse width is T₁ is the first state, a state in which the additional light source 101 is turned off and the pulse width is T₂ is the second state, a state in which the additional light source 101 is turned off and the pulse width is T is the fifth state, a state in which the additional light source 101 is turned on and the pulse width is T₃ is the third state, a state in which the additional light source 101 is turned on and the pulse width is T₄ is the fourth state, and a state in which the additional light source 101 is turned on and the pulse width is T is the sixth state.

However, when the additional light source 101 is turned on in step S121 in FIG. 8, after the discharge probability ²P is calculated, the discharge probability calculating portion 202 a needs to instruct the light source control portion 21 to turn off the additional light source 101.

In the first and second embodiments, the case where the light source 100 is a flame is described as an example, but the light detection system of the present disclosure can be applied to the light source 100 other than a flame.

The sensitivity parameter storing portion 19 and the central processing portions 20 and 20 a described in the first and second embodiments can be implemented by a computer including a central processing unit (CPU), a storage device, and an interface, and a program configured to control these hardware resources.

A configuration example of the computer is illustrated in FIG. 9. The computer includes a CPU 300, a storage device 301, and an interface device (I/F) 302. To the I/F 302, the application voltage generating circuit 12, the rectangular pulse generating portions 17 and 17 a, the A/D converting portion 18, the light source control portion 21, and the like are connected. In the computer described above, a program for causing the computer to achieve a discharge probability calculating method and a received light quantity measuring method according to the present disclosure is stored in the storage device 301. The CPU 300 executes the processes described in the first and second embodiments in accordance with the program stored in the storage device 301.

INDUSTRIAL APPLICABILITY

The present disclosure can be applied to a light detection system. Further, the present disclosure can also be applied to detection of light other than a flame.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

1: optical sensor, 2: external power supply, 3, 3 a: calculating device, 11: power supply circuit, 12: application voltage generating circuit, 13: trigger circuit, 14: voltage dividing resistor, 15: current detecting circuit, 16, 16 a: processing circuit, 17, 17 a: rectangular pulse generating portion, 18: A/D converting portion, 19: sensitivity parameter storing portion, 20, 20 a: central processing portion, 21: light source control portion, 100: light source, 101: additional light source, 201: discharge determining portion, 202, 202 a, 203, 203 a: discharge probability calculating portion, 204: number-of-times-of-pulse-application accumulating portion, 205: number-of-times-of-application determining portion, 206: received light quantity calculating portion, 207: received light quantity determining portion 

1. A light detection system comprising: an optical sensor configured to detect light emitted from a first light source; a second light source having a known light quantity, which is installed such that generated light is incident on the optical sensor together with the light from the first light source; a light source control portion configured to control turning-on/turning-off of the second light source; an application voltage generating portion configured to periodically apply a drive pulse voltage to an electrode of the optical sensor; a current detecting portion configured to detect a discharge current of the optical sensor; a discharge determining portion configured to detect a discharge of the optical sensor based on the discharge current detected by the current detecting portion; a first discharge probability calculating portion configured to calculate a discharge probability based on the number of times of application of the drive pulse voltage applied by the application voltage generating portion and the number of times of discharge detected by the discharge determining portion during the application of the drive pulse voltage for each of a first state in which the second light source is turned on or turned off, a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state, a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as that of the first state, and a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is the same as that of the second state; a storing portion configured to store, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first and second states, and the third and fourth states; a second discharge probability calculating portion configured to calculate a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the first, second, third, and fourth states, and the pulse widths of the drive pulse voltage in the first, second, third, and fourth states; and a received light quantity calculating portion configured to calculate the received light quantity received by the optical sensor in the first and second states or the third and fourth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the first, second, third, and fourth states, the pulse widths of the drive pulse voltage in the first, second, third, and fourth states, and the discharge probabilities calculated by the second discharge probability calculating portion.
 2. The light detection system according to claim 1, wherein the second discharge probability calculating portion is configured to calculate a discharge probability P_(aA) of the regular discharge by using $P_{aA} = {1 - \left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{- \frac{Q_{0}T_{0}}{{({T_{1} - T_{2}})}{({Q_{1} - Q_{2}})}}}}$ and calculate a discharge probability P_(bA) of the irregular discharge by using $P_{bA} = {1 - \left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{- \frac{T_{1}}{({T_{1} - T_{2}})}} \cdot \frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}}}$ or $P_{bA} = {1 - \left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{- \frac{T_{1}}{({T_{1} - T_{2}})}} \cdot \frac{1 - {\,_{2}^{1}P}}{1 - {\,_{2}^{2}P}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}}}$ where T₀ is the reference pulse width of the drive pulse voltage, Q₀ is the reference received light quantity received by the optical sensor, Q₁−Q₂ is the difference in received light quantity received by the optical sensor between the first and second states and the third and fourth states, ¹ ₁P is the discharge probability calculated by the first discharge probability calculating portion in the first state, ¹ ₂P is the discharge probability calculated by the first discharge probability calculating portion in the second state, ² ₁P is the discharge probability calculated by the first discharge probability calculating portion in the third state, ² ₂P is the discharge probability calculated by the first discharge probability calculating portion in the fourth state, T₁ is the pulse width of the drive pulse voltage in the first and third states, T₂ is the pulse width of the drive pulse voltage in the second and fourth states, P_(aA) is the discharge probability of the regular discharge, P_(bA) is the discharge probability of the irregular discharge, and Q is the received light quantity received by the optical sensor in the first and second states or the third and fourth states, and the received light quantity calculating portion is configured to calculate the received light quantity Q by using ${\left( {1 - P_{aA}} \right)^{\frac{T_{1}}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)} = \left( \frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \right)^{\frac{Q}{Q_{1} - Q_{2}}}$ ${{{or}\left( {1 - P_{aA}} \right)}^{\frac{T_{2}}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)} = {\left( \frac{1 - {\,_{2}^{1}P}}{1 - {\,_{2}^{2}P}} \right)^{\frac{Q}{Q_{1} - Q_{2}}}.}$
 3. A light detection system comprising: an optical sensor configured to detect light emitted from a first light source; a second light source having a known light quantity, which is installed such that generated light is incident on the optical sensor together with the light from the first light source; a light source control portion configured to control turning-on/turning-off of the second light source; an application voltage generating portion configured to periodically apply a drive pulse voltage to an electrode of the optical sensor; a current detecting portion configured to detect a discharge current of the optical sensor; a discharge determining portion configured to detect a discharge of the optical sensor based on the discharge current detected by the current detecting portion; a first discharge probability calculating portion configured to calculate a discharge probability based on the number of times of application of the drive pulse voltage applied by the application voltage generating portion and the number of times of discharge detected by the discharge determining portion during the application of the drive pulse voltage for each of a first state in which the second light source is turned on or turned off, a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state, a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as that of the first state, a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is the same as that of the second state, a fifth state in which a turning-on/turning-off state of the second light source is the same as that of the first and second states, and a pulse width of the drive pulse voltage is the same as that of either the first and third states or the second and fourth states, or different from that of all of the first, second, third, and fourth states, and a sixth state in which a turning-on/turning-off state of the second light source is the same as that of the third and fourth states and a pulse width of the drive pulse voltage is the same as that of the fifth state; a storing portion configured to store, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first, second, and fifth states, and the third, fourth, and sixth states; a second discharge probability calculating portion configured to calculate a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the first, second, third, fourth, fifth, and sixth states, and the pulse widths of the drive pulse voltage in the first, second, third, fourth, fifth, and sixth states; and a received light quantity calculating portion configured to calculate the received light quantity received by the optical sensor in the fifth and sixth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the fifth and sixth states, the pulse widths of the drive pulse voltage in the fifth and sixth states, and the discharge probabilities calculated by the second discharge probability calculating portion.
 4. The light detection system according to claim 3, wherein the second discharge probability calculating portion is configured to calculate a discharge probability P_(aA) of the regular discharge by using $P_{aA} = {1 - \left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{1}^{2}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{\frac{Q_{0}T_{0}}{{({T_{1} - T_{2}})}{({Q_{1} - Q_{2}})}}}}$ and calculate a discharge probability P_(bA) of the irregular discharge by using $P_{bA} = {1 - \left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{2}^{2}P}}{1 - {\,_{2}^{1}P}}} \right)^{- \frac{T}{({T_{1} - T_{2}})}} \cdot \frac{1 - {\,^{1}P}}{1 - {\,^{2}P}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}}}$ where T₀ is the reference pulse width of the drive pulse voltage, Q₀ is the reference received light quantity received by the optical sensor, Q₁−Q₂ is the difference in received light quantity received by the optical sensor between the first, second, and fifth states and the third, fourth, and sixth states, ¹ ₁P is the discharge probability calculated by the first discharge probability calculating portion in the first state, ¹ ₂P is the discharge probability calculated by the first discharge probability calculating portion in the second state, ² ₁P is the discharge probability calculated by the first discharge probability calculating portion in the third state, ² ₂P is the discharge probability calculated by the first discharge probability calculating portion in the fourth state, ¹P is the discharge probability calculated by the first discharge probability calculating portion in the fifth state, ²P is the discharge probability calculated by the first discharge probability calculating portion in the sixth state, T₁ is the pulse width of the drive pulse voltage in the first and third states, T₂ is the pulse width of the drive pulse voltage in the second and fourth states, T is the pulse width of the drive pulse voltage in the fifth and sixth states, P_(aA) is the discharge probability of the regular discharge, P_(bA) is the discharge probability of the irregular discharge, and Q is the received light quantity received by the optical sensor in the fifth and sixth states, and the received light quantity calculating portion is configured to calculate the received light quantity Q by using ${\left( {1 - P_{aA}} \right)^{\frac{T}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)} = {\left( \frac{1 - {\,^{1}P}}{1 - {\,^{2}P}} \right)^{\frac{Q}{Q_{1} - Q_{2}}}.}$
 5. A light detection system comprising: an optical sensor configured to detect light emitted from a first light source; a second light source having a known light quantity, which is installed such that generated light is incident on the optical sensor together with the light from the first light source; a light source control portion configured to control turning-on/turning-off of the second light source; an application voltage generating portion configured to periodically apply a drive pulse voltage to an electrode of the optical sensor; a current detecting portion configured to detect a discharge current of the optical sensor; a discharge determining portion configured to detect a discharge of the optical sensor based on the discharge current detected by the current detecting portion; a first discharge probability calculating portion configured to calculate a discharge probability based on the number of times of application of the drive pulse voltage applied by the application voltage generating portion and the number of times of discharge detected by the discharge determining portion during the application of the drive pulse voltage for each of a first state in which the second light source is turned on or turned off, a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state, a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as or different from that of the first state, a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is different from that of the third state, a fifth state in which a turning-on/turning-off state of the second light source is the same as that of the first and second states and a pulse width of the drive pulse voltage is the same as that of at least one of the first, second, third, and fourth states or different from that of all of the first, second, third, and fourth states, and a sixth state in which a turning-on/turning-off state of the second light source is the same as that of the third and fourth states and a pulse width of the drive pulse voltage is the same as that of the fifth state; a storing portion configured to store, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first, second, and fifth states, and the third, fourth, and sixth states; and a second discharge probability calculating portion configured to calculate a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the first, second, third, fourth, fifth, and sixth states, and the pulse widths of the drive pulse voltage in the first, second, fifth, and sixth states under a condition that a difference in pulse width between the first state and the second state is equal to a difference in pulse width between the third state and the fourth state.
 6. The light detection system according to claim 5, further comprising: a received light quantity calculating portion configured to calculate the received light quantity received by the optical sensor in the fifth and sixth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated by the first discharge probability calculating portion in the fifth and sixth states, the pulse widths of the drive pulse voltage in the fifth and sixth states, and the discharge probabilities calculated by the second discharge probability calculating portion.
 7. The light detection system according to claim 5, wherein the second discharge probability calculating portion is configured to calculate a discharge probability P_(aA) of the regular discharge by using $P_{aA} = {1 - \left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} \right)^{\frac{Q_{0}}{{({Q_{1} - Q_{2}})}{({T_{1} - T_{2}})}}}}$ and calculate a discharge probability P_(bA) of the irregular discharge by using $P_{bA} = {1 - \left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} \right)^{- \frac{T}{{({T_{1} - T_{2}})}T_{0}}} \cdot \frac{1 - {\,^{1}P}}{1 - {\,^{2}P}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}}}$ where T₀ is the reference pulse width of the drive pulse voltage, Q₀ is the reference received light quantity received by the optical sensor, Q₁−Q₂ is the difference in received light quantity received by the optical sensor between the first, second, and fifth states and the third, fourth, and sixth states, ¹ ₁P is the discharge probability calculated by the first discharge probability calculating portion in the first state, ¹ ₂P is the discharge probability calculated by the first discharge probability calculating portion in the second state, ² ₃P is the discharge probability calculated by the first discharge probability calculating portion in the third state, ² ₄P is the discharge probability calculated by the first discharge probability calculating portion in the fourth state, ¹P is the discharge probability calculated by the first discharge probability calculating portion in the fifth state, ²P is the discharge probability calculated by the first discharge probability calculating portion in the sixth state, T₁ is the pulse width of the drive pulse voltage in the first and third states, T₂ is the pulse width of the drive pulse voltage in the second and fourth states, T is the pulse width of the drive pulse voltage in the fifth and sixth states, P_(aA) is the discharge probability of the regular discharge, and P_(bA) is the discharge probability of the irregular discharge.
 8. The light detection system according to claim 6, wherein the second discharge probability calculating portion is configured to calculate a discharge probability P_(aA) of the regular discharge by using $P_{aA} = {1 - \left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} \right)^{\frac{Q_{0}}{{({Q_{1} - Q_{2}})}{({T_{1} - T_{2}})}}}}$ and calculate a discharge probability P_(bA) of the irregular discharge by using $P_{bA} = {1 - \left( {\left( {\frac{1 - {\,_{1}^{1}P}}{1 - {\,_{2}^{1}P}} \cdot \frac{1 - {\,_{4}^{2}P}}{1 - {\,_{3}^{2}P}}} \right)^{- \frac{T}{{({T_{1} - T_{2}})}T_{0}}} \cdot \frac{1 - {\,^{1}P}}{1 - {\,^{2}P}}} \right)^{\frac{Q_{0}}{Q_{1} - Q_{2}}}}$ where T₀ is the reference pulse width of the drive pulse voltage, Q₀ is the reference received light quantity received by the optical sensor, Q₁−Q₂ is the difference in received light quantity received by the optical sensor between the first, second, and fifth states and the third, fourth, and sixth states, ¹ ₁P is the discharge probability calculated by the first discharge probability calculating portion in the first state, ¹ ₂P is the discharge probability calculated by the first discharge probability calculating portion in the second state, ² ₃P is the discharge probability calculated by the first discharge probability calculating portion in the third state, ² ₄P is the discharge probability calculated by the first discharge probability calculating portion in the fourth state, ¹P is the discharge probability calculated by the first discharge probability calculating portion in the fifth state, ²P is the discharge probability calculated by the first discharge probability calculating portion in the sixth state, T₁ is the pulse width of the drive pulse voltage in the first and third states, T₂ is the pulse width of the drive pulse voltage in the second and fourth states, T is the pulse width of the drive pulse voltage in the fifth and sixth states, P_(aA) is the discharge probability of the regular discharge, and P_(bA) is the discharge probability of the irregular discharge.
 9. The light detection system according to claim 6, wherein the received light quantity calculating portion is configured to calculate the received light quantity Q by using ${\left( {1 - P_{aA}} \right)^{\frac{T}{T_{0}}} \cdot \left( {1 - P_{bA}} \right)} = \left( \frac{1 - {\,^{1}P}}{1 - {\,^{2}P}} \right)^{\frac{Q}{Q_{1} - Q_{2}}}$ where T₀ is the reference pulse width of the drive pulse voltage, Q₀ is the reference received light quantity received by the optical sensor, Q₁−Q₂ is the difference in received light quantity received by the optical sensor between the first, second, and fifth states and the third, fourth, and sixth states, ¹P is the discharge probability calculated by the first discharge probability calculating portion in the fifth state, ²P is the discharge probability calculated by the first discharge probability calculating portion in the sixth state, T is the pulse width of the drive pulse voltage in the fifth and sixth states, P aA is the discharge probability of the regular discharge calculated by the second discharge probability calculating portion, P_(bA) is the discharge probability of the irregular discharge calculated by the second discharge probability calculating portion, and Q is the received light quantity received by the optical sensor in the fifth and sixth states.
 10. A received light quantity measuring method of a light detection system, the method comprising: a first step of periodically applying a drive pulse voltage to an electrode of an optical sensor that detects light emitted from a first light source in a first state in which light from a second light source having a known light quantity is incident on the optical sensor or the second light source is turned off; a second step of detecting a discharge current of the optical sensor in the first state; a third step of detecting a discharge of the optical sensor based on the discharge current in the first state; a fourth step of calculating a discharge probability in the first state based on the number of times of application of the drive pulse voltage applied in the first step and the number of times of discharge detected in the third step during the application of the drive pulse voltage; a fifth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state; a sixth step of detecting a discharge current of the optical sensor in the second state; a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state; an eighth step of calculating a discharge probability in the second state based on the number of times of application of the drive pulse voltage applied in the fifth step and the number of times of discharge detected in the seventh step during the application of the drive pulse voltage; a ninth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as that of the first state; a tenth step of detecting a discharge current of the optical sensor in the third state; an eleventh step of detecting a discharge of the optical sensor based on the discharge current in the third state; a twelfth step of calculating a discharge probability in the third state based on the number of times of application of the drive pulse voltage applied in the ninth step and the number of times of discharge detected in the eleventh step during the application of the drive pulse voltage; a thirteenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is the same as that of the second state; a fourteenth step of detecting a discharge current of the optical sensor in the fourth state; a fifteenth step of detecting a discharge of the optical sensor based on the discharge current in the fourth state; a sixteenth step of calculating a discharge probability in the fourth state based on the number of times of application of the drive pulse voltage applied in the thirteenth step and the number of times of discharge detected in the fifteenth step during the application of the drive pulse voltage; a seventeenth step of referring to a storing portion that stores, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first and second states and the third and fourth states, and calculating a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth, eighth, twelfth, and sixteenth steps, and the pulse widths of the drive pulse voltage in the first, second, third, and fourth states; and an eighteenth step of calculating the received light quantity received by the optical sensor in the first and second states or the third and fourth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth, eighth, twelfth, and sixteenth steps, the pulse widths of the drive pulse voltage in the first, second, third, and fourth states, and the discharge probabilities calculated in the seventeenth step.
 11. A received light quantity measuring method of a light detection system, the method comprising: a first step of periodically applying a drive pulse voltage to an electrode of an optical sensor that detects light emitted from a first light source in a first state in which light from a second light source having a known light quantity is incident on the optical sensor or the second light source is turned off; a second step of detecting a discharge current of the optical sensor in the first state; a third step of detecting a discharge of the optical sensor based on the discharge current in the first state; a fourth step of calculating a discharge probability in the first state based on the number of times of application of the drive pulse voltage applied in the first step and the number of times of discharge detected in the third step during the application of the drive pulse voltage; a fifth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state; a sixth step of detecting a discharge current of the optical sensor in the second state; a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state; an eighth step of calculating a discharge probability in the second state based on the number of times of application of the drive pulse voltage applied in the fifth step and the number of times of discharge detected in the seventh step during the application of the drive pulse voltage; a ninth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as that of the first state; a tenth step of detecting a discharge current of the optical sensor in the third state; an eleventh step of detecting a discharge of the optical sensor based on the discharge current in the third state; a twelfth step of calculating a discharge probability in the third state based on the number of times of application of the drive pulse voltage applied in the ninth step and the number of times of discharge detected in the eleventh step during the application of the drive pulse voltage; a thirteenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is the same as that of the second state; a fourteenth step of detecting a discharge current of the optical sensor in the fourth state; a fifteenth step of detecting a discharge of the optical sensor based on the discharge current in the fourth state; a sixteenth step of calculating a discharge probability in the fourth state based on the number of times of application of the drive pulse voltage applied in the thirteenth step and the number of times of discharge detected in the fifteenth step during the application of the drive pulse voltage; a seventeenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fifth state in which a turning-on/turning-off state of the second light source is the same as that of the first and second states and a pulse width of the drive pulse voltage is the same as that of either the first and third states or the second and fourth states, or different from that of all of the first, second, third, and fourth states; an eighteenth step of detecting a discharge current of the optical sensor in the fifth state; a nineteenth step of detecting a discharge of the optical sensor based on the discharge current in the fifth state; a twentieth step of calculating a discharge probability in the fifth state based on the number of times of application of the drive pulse voltage applied in the seventeenth step and the number of times of discharge detected in the nineteenth step during the application of the drive pulse voltage; a twenty-first step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a sixth state in which a turning-on/turning-off state of the second light source is the same as that of the third and fourth states and a pulse width of the drive pulse voltage is the same as that of the fifth state; a twenty-second step of detecting a discharge current of the optical sensor in the sixth state; a twenty-third step of detecting a discharge of the optical sensor based on the discharge current in the sixth state; a twenty-fourth step of calculating a discharge probability in the sixth state based on the number of times of application of the drive pulse voltage applied in the twenty-first step and the number of times of discharge detected in the twenty-third step during the application of the drive pulse voltage; a twenty-fifth step of referring to a storing portion that stores, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first, second, and fifth states and the third, fourth, and sixth states, and calculating a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth, eighth, twelfth, sixteenth, twentieth, and twenty-fourth steps, and the pulse widths of the drive pulse voltage in the first, second, third, fourth, fifth, and sixth states; and a twenty-sixth step of calculating the received light quantity received by the optical sensor in the fifth and sixth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the twentieth and twenty-fourth steps, the pulse widths of the drive pulse voltage in the fifth and sixth states, and the discharge probabilities calculated in the twenty-fifth step.
 12. A discharge probability calculating method of a light detection system, the method comprising: a first step of periodically applying a drive pulse voltage to an electrode of an optical sensor that detects light emitted from a first light source in a first state in which light from a second light source having a known light quantity is incident on the optical sensor or the second light source is turned off; a second step of detecting a discharge current of the optical sensor in the first state; a third step of detecting a discharge of the optical sensor based on the discharge current in the first state; a fourth step of calculating a discharge probability in the first state based on the number of times of application of the drive pulse voltage applied in the first step and the number of times of discharge detected in the third step during the application of the drive pulse voltage; a fifth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state; a sixth step of detecting a discharge current of the optical sensor in the second state; a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state; an eighth step of calculating a discharge probability in the second state based on the number of times of application of the drive pulse voltage applied in the fifth step and the number of times of discharge detected in the seventh step during the application of the drive pulse voltage; a ninth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as or different from that of the first state; a tenth step of detecting a discharge current of the optical sensor in the third state; an eleventh step of detecting a discharge of the optical sensor based on the discharge current in the third state; a twelfth step of calculating a discharge probability in the third state based on the number of times of application of the drive pulse voltage applied in the ninth step and the number of times of discharge detected in the eleventh step during the application of the drive pulse voltage; a thirteenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is different from that of the third state; a fourteenth step of detecting a discharge current of the optical sensor in the fourth state; a fifteenth step of detecting a discharge of the optical sensor based on the discharge current in the fourth state; a sixteenth step of calculating a discharge probability in the fourth state based on the number of times of application of the drive pulse voltage applied in the thirteenth step and the number of times of discharge detected in the fifteenth step during the application of the drive pulse voltage; a seventeenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fifth state in which a turning-on/turning-off state of the second light source is the same as that of the first and second states and a pulse width of the drive pulse voltage is the same as that of at least one of the first, second, third, and fourth states or different from that of all of the first, second, third, and fourth states; an eighteenth step of detecting a discharge current of the optical sensor in the fifth state; a nineteenth step of detecting a discharge of the optical sensor based on the discharge current in the fifth state; a twentieth step of calculating a discharge probability in the fifth state based on the number of times of application of the drive pulse voltage applied in the seventeenth step and the number of times of discharge detected in the nineteenth step during the application of the drive pulse voltage; a twenty-first step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a sixth state in which a turning-on/turning-off state of the second light source is the same as that of the third and fourth states and a pulse width of the drive pulse voltage is the same as that of the fifth state; a twenty-second step of detecting a discharge current of the optical sensor in the sixth state; a twenty-third step of detecting a discharge of the optical sensor based on the discharge current in the sixth state; a twenty-fourth step of calculating a discharge probability in the sixth state based on the number of times of application of the drive pulse voltage applied in the twenty-first step and the number of times of discharge detected in the twenty-third step during the application of the drive pulse voltage; and a twenty-fifth step of referring to a storing portion that stores, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first, second, and fifth states and the third, fourth, and sixth states, and calculating a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth, eighth, twelfth, sixteenth, twentieth, and twenty-fourth steps, and the pulse widths of the drive pulse voltage in the first, second, fifth, and sixth states under a condition that a difference in pulse width between the first state and the second state is equal to a difference in pulse width between the third state and the fourth state.
 13. A received light quantity measuring method of a light detection system, the method comprising: a first step of periodically applying a drive pulse voltage to an electrode of an optical sensor that detects light emitted from a first light source in a first state in which light from a second light source having a known light quantity is incident on the optical sensor or the second light source is turned off; a second step of detecting a discharge current of the optical sensor in the first state; a third step of detecting a discharge of the optical sensor based on the discharge current in the first state; a fourth step of calculating a discharge probability in the first state based on the number of times of application of the drive pulse voltage applied in the first step and the number of times of discharge detected in the third step during the application of the drive pulse voltage; a fifth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a second state in which a turning-on/turning-off state of the second light source is the same as that of the first state and a pulse width of the drive pulse voltage is different from that of the first state; a sixth step of detecting a discharge current of the optical sensor in the second state; a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state; an eighth step of calculating a discharge probability in the second state based on the number of times of application of the drive pulse voltage applied in the fifth step and the number of times of discharge detected in the seventh step during the application of the drive pulse voltage; a ninth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a third state in which a turning-on/turning-off state of the second light source is different from that of the first and second states and a pulse width of the drive pulse voltage is the same as or different from that of the first state; a tenth step of detecting a discharge current of the optical sensor in the third state; an eleventh step of detecting a discharge of the optical sensor based on the discharge current in the third state; a twelfth step of calculating a discharge probability in the third state based on the number of times of application of the drive pulse voltage applied in the ninth step and the number of times of discharge detected in the eleventh step during the application of the drive pulse voltage; a thirteenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fourth state in which a turning-on/turning-off state of the second light source is the same as that of the third state and a pulse width of the drive pulse voltage is different from that of the third state; a fourteenth step of detecting a discharge current of the optical sensor in the fourth state; a fifteenth step of detecting a discharge of the optical sensor based on the discharge current in the fourth state; a sixteenth step of calculating a discharge probability in the fourth state based on the number of times of application of the drive pulse voltage applied in the thirteenth step and the number of times of discharge detected in the fifteenth step during the application of the drive pulse voltage; a seventeenth step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a fifth state in which a turning-on/turning-off state of the second light source is the same as that of the first and second states and a pulse width of the drive pulse voltage is the same as that of at least one of the first, second, third, and fourth states or different from that of all of the first, second, third, and fourth states; an eighteenth step of detecting a discharge current of the optical sensor in the fifth state; a nineteenth step of detecting a discharge of the optical sensor based on the discharge current in the fifth state; a twentieth step of calculating a discharge probability in the fifth state based on the number of times of application of the drive pulse voltage applied in the seventeenth step and the number of times of discharge detected in the nineteenth step during the application of the drive pulse voltage; a twenty-first step of periodically applying the drive pulse voltage to the electrode of the optical sensor in a sixth state in which a turning-on/turning-off state of the second light source is the same as that of the third and fourth states and a pulse width of the drive pulse voltage is the same as that of the fifth state; a twenty-second step of detecting a discharge current of the optical sensor in the sixth state; a twenty-third step of detecting a discharge of the optical sensor based on the discharge current in the sixth state; a twenty-fourth step of calculating a discharge probability in the sixth state based on the number of times of application of the drive pulse voltage applied in the twenty-first step and the number of times of discharge detected in the twenty-third step during the application of the drive pulse voltage; a twenty-fifth step of referring to a storing portion that stores, in advance as known sensitivity parameters of the optical sensor, a reference pulse width of the drive pulse voltage, a reference received light quantity received by the optical sensor, and a difference in received light quantity received by the optical sensor between the first, second, and fifth states and the third, fourth, and sixth states, and calculating a discharge probability of a regular discharge when the pulse width of the drive pulse voltage is the reference pulse width and the received light quantity received by the optical sensor is the reference received light quantity, and a discharge probability of an irregular discharge caused by a noise component other than a discharge occurring due to a photoelectric effect of the optical sensor, which occurs without depending on the pulse width of the drive pulse voltage and which occurs depending on the received light quantity received by the optical sensor, based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the fourth, eighth, twelfth, sixteenth, twentieth, and twenty-fourth steps, and the pulse widths of the drive pulse voltage in the first, second, fifth, and sixth states under a condition that a difference in pulse width between the first state and the second state is equal to a difference in pulse width between the third state and the fourth state; and a twenty-sixth step of calculating the received light quantity received by the optical sensor in the fifth and sixth states based on the sensitivity parameters stored in the storing portion, the discharge probabilities calculated in the twentieth and twenty-fourth steps, the pulse widths of the drive pulse voltage in the fifth and sixth states, and the discharge probabilities calculated in the twenty-fifth step. 